Thread: Human Brain

I start this subject because I would like to understand better Human intelligence and simply how the brain works..... i know the basics that the brain as millions of neurons and that the information is passed through the Aaxon as electric signals and crosses the dendrites through hormone reaction but my question is of what it consists This Information and how does the brain transform into Thoughts, Words, Imagination.... Please someone ease my trobled mind

if someone finds out, can they let me know too ?

i can only assume that neuroscience is working towards an answer to the questions that trouble you, but i'm equally sure that neuroscientists are still a long way off a satisfactory answer to them

i'm fairly sure that memories are volatile and less volatile chemicals for short and long-term memory respectively, and that some chemical trigger duplicates items from long-term memory for use in our equivalent of a CPU, but apart from that i don't have a clue

New Scientist recently had an interesting article on how genius depends on being in a "state of self-organised criticality", i.e. it operates at the edge of chaos and flashes of inspiration are short bouts of chaos followed by re-establishment of order

Originally Posted by Aeon

I start this subject because I would like to understand better Human intelligence and simply how the brain works..... i know the basics that the brain as millions of neurons and that the information is passed through the Aaxon as electric signals and crosses the dendrites through hormone reaction but my question is of what it consists This Information and how does the brain transform into Thoughts, Words, Imagination.... Please someone ease my trobled mind

I'd like to try, It might be that our electrical siganals are actually "empty slates" of energy that can be converted to whatever our brain wats or needs oin order to corrrectly analize and understand what is going on. This blank slate might be actually needed in order for thougth to even form like dough needed to make cake, so when these blanks reach it is then combined the questions that are present. such as what is the smell of the cake (but is obviously might be processed ina subconcious level because conciously we already know what the smell is) onced combined this slate transforms or should I say goes through somekind of "evolution" into a complete processed thought like hapiness, boredom, exitedness etc. I really hope i am not soo wrong and Iwill get clowned by many, oh man i am new too lol I think I am wrong oh no no!!!! hEHEHE!!

If I may join, as complex as the intricacies of the human brain may seem, understanding its complexities became clearer to me while researching the evolution of the dreaming brain. When we examine and clearly understand the steps leading from primodial bacteria (photoautotrophs) to telencephalic function, I think we get of sense of what constitute the nature of thought, mind, and consciousness. There is more than sufficient evidence in brain injury and cross-species comparative studies to determine more about the true nature of brain processes and function than mainstream thought suggests. For example, There is evidence suggesting that the primary processes that constitute a mind evolved with the thalamus at the pinnacle of brainstem evolution. Further still, the neocortex may be little more than a sophistocated memory storage device that thalamic function uses to attenuate the thought processes it appears to generate. When the thalamus evolved, ancestral animals began to evolve the ability to engage behaviors independent of instinct. When we look at the neural developments that preceded thalamic evolution, we also get a sense of why its evolution became so crucial to the proactive thought processes that constitute the nature of mind. When we strip away the cortex and consider the structural nature of the thalamus, we see that it is remarkably similar to the cortex in structure with a right and left hemisphere and hemisphere adhesion. This similarity is no coincidence. There is a reason why all sensory information, with the exception of olfactory, must enter the thalamus first before reaching the cortex. The thalamus marks that stage in our evolution when our central nervous system began to produce a rudimentary mind. In my opinion, the function of the thalamus defines the very nature of a mind.

Originally Posted by DrmDoc

If I may join, as complex as the intricacies of the human brain may seem, understanding its complexities became clearer to me while researching the evolution of the dreaming brain. When we examine and clearly understand the steps leading from primodial bacteria (photoautotrophs) to telencephalic function, I think we get of sense of what constitute the nature of thought, mind, and consciousness. There is more than sufficient evidence in brain injury and cross-species comparative studies to determine more about the true nature brain processes and function than mainstream thought suggests. For example, There is evidence suggesting that the primary processes that constitute a mind evolved with the thalamus at the pinnacle of brainstem evolution. Further still, the neocortex may be little more than a sophistocated memory storage device that thalamic function uses to attenuate the thought processes it appears to generate. When the thalamus evolved, ancestral animals began to evolve the ability to engage behaviors independent instinct. When we look at the neural developments that preceded thalamic evolution, we also get a sense of why its evolution became so crucial to the proactive thought processes that constitute the nature of mind. When we strip away the cortex and consider the structural nature of the thalamus, we see that it is remarkable similar to the cortex in structure with a right and left hemisphere and hemisphere adhesion. This similarity is no coincidence. There is a reason why all sensory information, with the exception of olfactory, must enter the thalamus first before reaching the cortex. The thalamus mark that stage in our evolution when our central nervous system began to produce a rudimentary mind. In my opinion, the function of the thalamus defines the very nature of a mind.

I knew this forum was somewhat intense for me!

Do any of uguys think I made any kind of sense at all? pelase tell me, your analysis counts
thanks

Originally Posted by scientia

Do any of uguys think I made any kind of sense at all? pelase tell me, your analysis counts
thanks

It doesn't seem to reflect real psychology, anatomy or physics. Contributions should be limited to subjects that one has a reasonable grasp on. Pure speculation is to be avoided. It's also difficult to understand the meaning with the spelling errors. There's no urgency to respond.

How is it done? Well, how does Alyx Vance "know" where to run and what to shoot when you play a game of Half Life 2?

How does your computer actually compute? 01101111 - that's how. On - Off, yes-no.

A Neuron fires or receives, or is silent. It receives a signal, and based on its strength/location, shoots off another signal modified in strength by its own internal instructions. Short, simple, small, so far as we huge animals vs the cell are concerned.

Add up millions of these firings at once and you get one hell of a cumulative effect, eh? Go look at a pic of some hot chix's cleavage and see what the net firing result of your neurons are. Guess which of your many different 'job description' neurons are firing off: the intellectual ones, or the instinctual ones (to name only two)?

Originally Posted by Aeon

I start this subject because I would like to understand better Human intelligence and simply how the brain works..... i know the basics that the brain as millions of neurons and that the information is passed through the Aaxon as electric signals and crosses the dendrites through hormone reaction but my question is of what it consists This Information and how does the brain transform into Thoughts, Words, Imagination.... Please someone ease my trobled mind

From the moment the cells starts to divide after fertilization of the ovum by the sperm cell, development of the yet to be brain is programmed by the DNA and also the environment. Every single electrochemical impulse represent specific information thus billions of these brain cells can create billions of probabilities of pathways which makes us unique in the way each of us think and process information. Hey, the picture of the real world that you're looking at now are just pieces of information built from electrochemical impulses in your brain. So what are you looking at really?

There are many types of nerve cells in the brain. If you take them individually, they may differ just in their morphology or chemical make up. But group them up, they serve a special function. Some parts of your brain are responsible for speech, sight, sound, taste, cognition, etc etc. All are affected by the combination of inherited gene and environment.

Does this make any sense?

When the thalamus evolved, ancestral animals began to evolve the ability to engage behaviors independent instinct.

Which animals did the thalamus first arise in? Can we know using the fossil record? I've heard of brain casings capturing the forms of brains but I usually only hear descriptions about the lobes.

Originally Posted by gottspieler

Which animals did the thalamus first arise in? Can we know using the fossil record? I've heard of brain casings capturing the forms of brains but I usually only hear descriptions about the lobes.

Although we cannot know in which animals the thalamus originated, the earliest endocast found was that of haikouella lanceolota, which suggested little more than a lump of neural ganglia anterior to notochord development. We know that when the thalamus evolved, ancestral animals were mentally able to do what they could not before by virtue of what contemporary comparative decorticate study has suggested among test animals. Without the thalamus, behaviors are more reflexsive and reactive to stimuli than directed and proactive. The emergence of the thalamus gave antecedant animals the ability to integrate multiple sources of sensory information in ways that permitted behaviors independent of those considered reactive or instinctive. Interestingly, the thalamus arises in our central nervous system (CNS) after the emergence of afferent neural developments associated with sight. Prior to sight, sensory information was primarily provided by tactile forms (taste, touch, and sound). We can verify this by where tactile forms of sensory afferents emerge in our CNS relative to visual sensory afferents. Sensory afferents rather than efferents is our primary measure of when ancestral animals developed certain attributes because they contiguously map the neural stages suggestive of sensory acquistion relative to associated behaviors. For example, the emergence of sound sensory afferents is indicative of the neural stage at which primitive animals obtain gross mobility because sound detection abilities suggest that they were physically orienting themselves either towards or opposite sources of sound. The neural cluster associated with sound arises in our CNS after those associated with taste and touch, and before those associated with sight. The idea that we can trace our brain's evolution by the emergence of sensory afferents is predicated on the idea that our brain structure retains the faint footprints of its evolutionary past as we are able to find in existing primitive animals many of the structure we find in the human brain. Interestingly, our CNS arises from a notochord stage align with existing primitive animals and suggestive of its ancient origins.

I read your question as being "how does my brain handle information? How does it understand it, and how does it communicate it?" Please, correct me if I'm wrong.

As an electrical and information engineer, I worked in computational neuroscience for a year. This is a thoroughly interesting field of study. How does the brain encode and decode information?

Let's start with your word "information". Information is mathematically defined as a 'reduction in entropy', or in easier language, a reduction in uncertainty. If I ask you "How are you", I am currently uncertain if you are happy ('1') or unhappy ('0'). If you tell me that you are happy, then you have given me one 'bit' of information. Eight bits makes a byte, and you are all familiar with the terms megabytes and gigabytes.

With this in mind, let's think about the brain. Computational neuroscientists imagine themselves as a little human sitting inside the brain, receiving electrical signals from nerve endings and sending commands out through nerve endings. As my advisor eloquently describes it: "The little fly sitting inside the fly's brain trying to fly the fly". From this viewpoint, you can intercept signals with an electrode and try to make predictions of the stimulus that caused that signal.

Information in the brain must be both transmitted and processed. Just like if I type 2+2= into my calculator, the command must be transmitted to the ALU (Arithmetic Logic Unit) chip, processed (=4), and then retransmitted back to the screen on my calculator to see the answer. Each neuron performs a transmission and processing task.

This is best demonstrated in the visual system. Because humans rely so heavily on vision, it is hardly surprising that our actions and memories are largely based on it. For this reason, vision is of great interest to neuroscientists, and we understand a *frightening* amount about exactly how our brain processes this information and how it stores it.

Light enters the eye, and is focussed on the retina by the lens. The light activates a protein called rhodopsin, and this causes a release of glutamate that causes a response in the secondary neurons: bipolar cells. The optic nerve does not have enough bandwidth (GBytes/second) to send all the information that the eye receives, so amazingly, the retina compresses the data right from the start. Each bipolar cell can be thought of as a 'pixel', but unlike our cameras, they are connected to many of their neighbours by "horizontal cells". They are connected in such a way that light arriving at a central region will induce a 'positive signal' while light arriving at surrounding photoreceptors will have a negative one. So if I'm looking at a purely white piece of paper, the net signal is zero, because all photoreceptors receive equal light and the positive and negative signals arriving at bipolar cells cancel out. Alternatively, if my piece of paper is one half black and one half white, then photoreceptors that are in the middle of the white area are off (the central and surrounding photoreceptors see white), and those in the middle of the black are off (for similar reasons), but those around the intersection of white and black have a signal: the positive/negative signals do not cancel out because more central photoreceptors see white than surrounding photoreceptors. The result is that *I have an edge detector*!! This circuitry transmits only what is really interesting in the visual scene: the boundaries of things.

This is an example of how clever neuron wiring can process information by integrating signals from different cells. Similar wiring patterns can perform subtractions, integrations and derivatives in our cortex. A final cool example of processing comes from a receptor called the NMDA receptor. This ion channel requires *both* an increase in potential and a neurotransmitter in order to signal. This system enables the computation of an 'AND' operation - a coincidence detector. I can now imagine a system where I have three neurons that are in close proximity forming a tri-synaptic region. Here, one neuron could signal whether the other two neurons should pass information between each other. This is exactly like a transistor in your computer.

But how does our brain *store* its processed information? The key to this is in synaptic plasticity. The process is called Hebbian Learning - if you want to look it up. The basic idea is that the more a synapse is used, the stronger it becomes. Many synapses exist that do not induce a change in potential in the next neuron. These 'silent synapses' are waiting to become active. Repeated action potentials arriving at the synapse will cause increases in calcium levels in the second neuron. This causes new receptors to be placed in the membrane of the second neuron, and now it responds to the first neuron firing by firing its own action potential! What we have done, is changed the wiring of a circuit in response to a stimulus. The state of this circuit (connected or not connected) and many other circuits can remember previous stimuli - aka a memory!

Finally, the brain is much cleverer than our computers. It has the ability to change its long-distance connections up to the age of 11 years. This is called the 'critical period' in humans, and it's when most learning occurs. Our brain can dramatically change its shape and wiring in this timeframe, facilitating huge amounts of memory formations and talent developments. Learning a language before age 11 is easier, and the accent is easier to perfect. After 11, our own language becomes hard-wired, and it becomes harder to learn. A great deal of research is going into reversing this process to facilitate adult learning. Interestingly, it is this inhibition of new outgrowth from axons that prevents regeneration of neurons in the brain after injury.

I hope this has been informative.

Originally Posted by marnixR

i.e. it operates at the edge of chaos and flashes of inspiration are short bouts of chaos followed by re-establishment of order

That sounds like me, apart form the re-establishment of order bit.

Originally Posted by Aeon

i know the basics that the brain as millions of neurons and that the information is passed through the Aaxon as electric signals and crosses the dendrites through hormone reaction but my question is of what it consists This Information and how does the brain transform into Thoughts, Words, Imagination.... Please someone ease my trobled mind

I think you are asking one of the more puzzling questions in neuroscience here. This gap between molecules, cells, synapses and emotions, facts and consciousness is very interesting.

How does one group translates in the other? They are so radically different and seem so distant from one another. How does a face, a smell, a feeling, and even an abstract concept can all be reduced to electric and chemical signals occurring among cells in the brain?

I think one of the candidate answers to this question has already been put forward by Mascott -- plasticity. The ability our brain cells have to reorganize the way they communicate with one another.

Take the visual stimulus of seeing a face for the first time, for instance. The light hits the retina, is translated into electric impulses, travels through the cells of the optical nerve, reaches the thalamus, then it's cascaded into the lateral geniculate nucleus, which in turn projects to the occipital lobe. At the occipital lobe the information is processed in an hierarchical fashion by the visual cortex starting at region V1.

Eventually it reaches another region in the temporal lobes called the fusiform gyrus, which is specialized in fine-processing visual inputs (like faces).

Now, the next time you see this face, the fusiform face area will probably analyze and compare the face you are seeing with previous faces that activated micro-circuitries in the region some time before. Because you have already been presented to this stimulus in the past, the cells in the FFA will now respond with much more intensity to it.

The more you see a face the more "familiar" it is to your brain, contrary to a face you only saw once. This phenomenon of increasingly sensibility to a stimulus is called plasticity.

Of course some cells in our brain are more sensitive to this habituation than others. It's much easier for a rat to learn how to associate an aversive feeling with a scenario than learning how to associate a task with a food reward, for instance. The neurons in the rat limbic system and basal ganglia (structures that play a role in mediating aversive stimuli learning) are probably much more prone to plasticity than the regions involved in learning tasks and associating them with positive rewards.

I think this sort of answers your question.

But what really amazes me is that you can evoke memories without the presence of any external stimuli. Just forget the light hitting the retina stuff, you can simply close your eyes and remember a face.

There have been experiments studying this, and in an fMRI scan it was observed that an image of a bedroom activated the same regions in the visual cortex as when the subject was asked to close his eyes and just imagine the bedroom. How does this happens? What region of our brain sends the command to the visual centers to reactivate a stimulus without the real presence of the stimulus? And how is it caused? If it is caused by something, does it mean we don't have free will?

Originally Posted by Kadu

But what really amazes me is that you can evoke memories without the presence of any external stimuli. Just forget the light hitting the retina stuff, you can simply close your eyes and remember a face.

I wonder if this is achieved using 'mirror neurons'. I'm not an expert in this concept, but I know they are neurons that fire when you watch someone perform a specific task (like throw a dart). They fire in a pattern that matches that of the neurons that would fire to really invoke a muscle response. This way, you 'practice' a response without actually performing it - like saying 'run it through in your head'.

So if you close your eyes and try and think of a face, do you have mirror neurons in or near the occipital lobe that correspond to the different angled-bars/edge detector neurons that fire when you see that face, which hook up to the same latter visual circuitry. So you really are 'seeing' that face, without the neurons in your real visual columns in the occipital lobe firing?

Could this firing pattern be remembered in the temporal lobe and fed back to the occipital lobe to make you think you are seeing the face? In this way, vision->memory->vision forms one big circuit -and forms the seat of our imagination?

It might be related to mirror neurons, but I don't think it is (big hunch here). I think it is more closely related to the micro circuitry of the neocortex than anything else. Neurons in layer 4 receive projections from the thalamus, then send the information to other layers which give rise the the awareness of a stimulus. But when you close your eyes and simply remembers a face the thalamus has no business in here, so neurons in layer 4 are getting information from somewhere else. The claustrum and other subcortical structures project to this layer, so there you go. Maybe something is happening here. After the stimulus reaches the cortex it gets in a loop, which means you'll get the very vivid sensory experience of seeing a face -- even though your eyes aren't seeing anything -- as far as the neurons there keep firing.

There is a lot of talk on the mirror neurons subject, but little is known about them. One of the most diffused hypothesis about these neurons is that they are responsible for our ability to put ourselves in the place of others, so it might be related to empathy, and this is somehow connected to what you proposed. The caveat here is that you must have some perceptive input in order to get mirror neurons to fire.

Mirror neurons have been studied more extensively in the rhesus monkey, where it has been documented that these cells fire when the animal grasps an object, but also fire when the animal observes a person grasping for the same object. These cells are really sophisticated however, and if you try to trick them by making the grasping movement but don't actually grasp anything, they refuse to fire. If the monkey sees you extending your arm to grasp something, but doesn't actually see what you are reaching for, the neurons also don't fire.

What these cells really give emergence to or if they have a role in imagination is a bit of a mystery as you can't ask a monkey to imagine something. Couple that to the fact that the techniques used to study it in animals (deep electrode readings) are different to the ones used in humans (mostly fMRI scans) and what you end up with is a lot of scientists doing more speculation than actual science.

Great response, Kadu. I know the anatomy of the neocortex well, but based off what you hunched, I'd like to read up more about exactly what the other layers in the cortical columns perform. It is known that long-term memory is stored diffusely in the cortex, and you can imagine imagination (!) is based largely off mashing different memories and experiences together so you actually 'sense' or 'feel' them. I wonder whether these computations are occuring in the same regions of the cortex as the actual sense is computed, but in a deeper cortical layer.

Neurosurgeons can often perform experiments on humans during brain surgery with consent. But needles can't be inserted into deep regions for mere experimental reasons due to higher risks. I know that the somatosensory and primary and secondary motor cortex were mapped out in this way.

Mascott, I believe they occur at the same cortical region. It's pretty funny you mentioned this, because I'm reading a book chapter right now that deals with the impact a single neuron stimulation has on neighbouring cells. Because some neurons have very sparsely distributed dendritric arborizations, they'll most probably make synaptic connections with cells in other layers too. So even though a neuron projects to a certain layer, the stimulus is not confined to that place only.

Here's a very interesting passage from the book, dealing exactly with imagination and recollection of past events:

Perhaps the most dramatic example of the impact of stimulating cortical
neurons occurs in humans during brain surgery to prevent epilepsy (Penfield
and Roberts 1959). Electrical stimulation was used to map out the cortical
regions that need to be spared during surgical resection, such as the language
areas (figure 19-1). Stimulation of cortical areas in awake patients sometimes
evoked sensory percepts and vivid recollections of past events:
When electrical stimulation recalls the past, the patient has what some of
them have called a "flash-back." He seems to re-live some previous period
of time and is aware of those things of which he was conscious in that previous
period. It is as though the stream of consciousness were flowing again
as it did once in the past. (p. 45)
These early studies used a crude surface electrode and high currents to
stimulate the cortex. This almost certainly resulted in current spread, so that
the actual neurons that were stimulated could not be determined (...)
http://papers.cnl.salk.edu/PDFs/What...02005-3873.pdf

Originally Posted by Kadu

Neurons in layer 4 receive projections from the thalamus, then send the information to other layers which give rise the the awareness of a stimulus. But when you close your eyes and simply remembers a face the thalamus has no business in here,...

If I may join your discussion, why? What is it about the nature of thalamic function that, in your opinion, suggests it does not contribute to facial imaging without sensory input? Have you considered your view of thalamic function relative to a functional perspective suggested by the evolutional path of our central nervous system?

Originally Posted by DrmDoc

Originally Posted by Kadu

Neurons in layer 4 receive projections from the thalamus, then send the information to other layers which give rise the the awareness of a stimulus. But when you close your eyes and simply remembers a face the thalamus has no business in here,...

If I may join your discussion, why? What is it about the nature of thalamic function that, in your opinion, suggests it does not contribute to facial imaging without sensory input? Have you considered your view of thalamic function relative to a functional perspective suggested by the evolutional path of our central nervous system?

And to further that, is it not the case that there are many many cortex-thalamus-cortex loops, and these are the hardest circuits to understand? I can imagine some of these relay loops playing a role in imagination. Perhaps as a way of connecting disparate concepts/regions?

Originally Posted by DrmDoc

If I may join your discussion, why? What is it about the nature of thalamic function that, in your opinion, suggests it does not contribute to facial imaging without sensory input? Have you considered your view of thalamic function relative to a functional perspective suggested by the evolutional path of our central nervous system?

Assuming that the concept of "imagination" is a very sophisticated cognitive process only possessed by higher mammals -- and maybe not even all primates -- we must take into account that neuroanatomical differences play a role in the emergence of this property. I believe that in lower mammals most of visual processing is done in thalamic regions, and only a small fraction of the input is sent to the cortex for further processing. In fact, in these animals the volume of the cortex is very small in proportion to the interbrain size.

There are cases where patients sustain lesions to the visual cortex, and although rendered technically blind by the damage, they still can recognize some visual inputs, specially the ones of motion nature (see "blindsight" for further reading). Their ability to recollect visual memories, however, is impaired. Damage to the fusyform gyrus also restrains the patient ability to recognize and recollect faces.

So I'm postulating here that the thalamus doesn't really play a very significative role in these more sofisticated "imagination" abilities of our mind. These are probably dealt mostly, but not only, by the neocortex.

Another compelling piece of data that corroborates this idea is the fact that the greatest volume of projections reaching the cortex originate from the cortex itself, and not from other external structures. The cortex is deeply interconnected with itself.

But of course there is evidence against this notion. I just learnt for instance that the cortico-thalamic connections in the cat's primary visual cortex outnumber the projections going in the other direction by a rate of 10:1. That is, there are more fibers sending information back to the thalamus than are fibers doing the opposite.

Sensory inputs from the specific modalities project from the thalamus to the middle layers (mainly layer 4) of the cortex. Reciprocal connections from each cortical area, mainly originating in deep layers, project back to the thalamus. In visual cortex of the cat it is known that the V1 projections back to the LGN of the thalamus outnumber thalamocortical projections by about 10:1.

Pages 40-42: http://abstract.cs.washington.edu/~m...eVision.94.pdf
*

Approaching the problem from an evolutionary perspective, we get another interesting fact against my hypothesis. The only sense that bypasses the thalamus is the sense of smell. Olfactory information is sent directly to an "older" cortex, where smells are processed. This is relevant because evoking smells is infinitely harder than evoking images, concepts or emotions. In fact, a whole plethora of sensations are simulated in our dreams -- guess which one is very rare to appear? That's right, smells and odors. So this somewhat supports the notion that the thalamus might play a whole in this inner blackboard we have in our minds.

Originally Posted by Kadu

Assuming that the concept of "imagination" is a very sophisticated cognitive process only possessed by higher mammals -- and maybe not even all primates -- we must take into account that neuroanatomical differences play a role in the emergence of this property.

I agree.

I believe that in lower mammals most of visual processing is done in thalamic regions, and only a small fraction of the input is sent to the cortex for further processing.

There are some studies, decorticate kitten studies particularly (as unpleasant as that may sound), suggesting that much of the visual field processing is retained without the visual cortex. However, this effect is not as prominent in mature decorticate cats presumably because of the hardwired dependency of thalamic function on cortical processing in adult cats.

In fact, in these animals the volume of the cortex is very small in proportion to the interbrain size.

This difference between cortical volume and interbrain size supports a distinction suggested by the relative factors effecting cortical evolution among species divergent from humanity. While researching brain evolution for a book I wrote a few years ago, it became clear to me that the cortical development among animals ancestral to humans might have been compelled by a disparity in their sensory acuity. In a nutshell, ancestral animals, akin to contemporary primates, may not have had the sensory acuity of the predators they likely encountered as the protection of their receding African rainforests surrendered to the perils of what may have been a rapidly expanding continental savannah. Consequently, our animal ancestors were probably compelled to reason beyond the limitation of their sensory to survive and compete against faster, stealthier, sensory superior animals.

Some believe that the differences in diet (as suggested by fossil teeth evidence) influenced the differences they discovered in brain size between primitive co-existent primate families. While some early primates may have been herbivores, some researchers believed that our ancestral primates began to eat meat and that this steady diet of protein enhanced their brain development. What these researchers failed to consider is the amount of reasoning and brainpower essential to procuring and maintaining a diet of meat compared to that required to obtain leaves, nuts, and roots. Essentially, when our ancestral primates began to eat meat, they had to reason how to compete with other, more skilled meat-eating animals to safely procure and maintain a source of sustenance that probably resisted being that source vigorously.

Foraging among the trees of what was once lush rainforests, early primates didn’t need the degree of visual, olfactory, and auditory acuity required of animals living in the flat, open grasslands of early Africa. Emerging from a retreating forest to a predator fraught savannah, early primates were likely forced to adapt beyond their sensory limitations to survive. Without sensory capabilities comparable to their savannah contemporaries, the competition, danger, fluid and varying circumstances associated with obtaining meat probably compelled our primate ancestors’ use of brainpower in ways not required by foraging. As we know, through contemporary brain study, sensory experience and learning stimulate brain growth and development. Rather than meat consumption itself, the mental demands associated with obtaining meat likely stimulated the larger brain developments we have found among the primates considered ancestral to humans. Consequently, our dependency on the sophisticated thought processes our primate ancestors evolved to survive distinguishes our larger cortical-to-interbrain size ratio over that of more sensory dependent animals—in my opinion.

There are cases where patients sustain lesions to the visual cortex, and although rendered technically blind by the damage, they still can recognize some visual inputs, specially the ones of motion nature (see "blindsight" for further reading). Their ability to recollect visual memories, however, is impaired.

I’ve read about these cases. I’ve also seen studies suggesting some visual acuity remains in test animals (rats and cats) after cortical ablations.

Damage to the fusyform gyrus also restrains the patient ability to recognize and recollect faces.

If I recall correctly, the fusiform gyrus is functionally associated with the medial temporal lobe, which could explain this diminished memory associated facial recognition ability.

So I'm postulating here that the thalamus doesn't really play a very significative role in these more sofisticated "imagination" abilities of our mind. These are probably dealt mostly, but not only, by the neocortex.

I disagee; the tenets of evolution, the contiguous structural and functional nature of our central nervous system (CNS), and the evidence decorticate study provides suggest to me that mind would not exist without thalamic function and input. If I may further explain:

A postulate of evolution suggests that the process of natural selection doesn’t discard past successful designs but rather builds upon those designs with succeeding structures that enhance the efficiency of prior successful designs. If this idea is valid, we should find some evidence of this building on prior structures in the design of contemporary brain structure. Further still, if our CNS evolved from an earlier design, we should find some evidence of that early design in brain structure as well.

When we evaluate the contiguous structural and functional design of our CNS from myelencephalon to telencephalon, we do indeed find some convincing evidence of a primitive-to-recent construct suggestive of successive enhancements to successful earlier designs. In the structural and functional neural design associated with taste afferents, for example, we find the less sophisticated afferent systems for the posterior tongue (Glossopharyngeal nerve) in the myelencephalon. Succeeding the myelencephalon contiguously, we find the more refined taste systems (Facial nerve) for the anterior tongue in the metencephalon. The posterior systems encompass 1/3 of the tongue, while the anterior encompasses 2/3. This kind of back-to-front, primitive-to-recent design is also suggested by the functional dynamics of subcortical/cortical structure.

In studies separating the cortex from subcortical structure (decortication), Dr. Michel Jouvet found that the neurally isolated cortex failed to register any activation throughout the survival period of test animals (Jouvet, M. and Jouvet D., "A study of the Neurophysiological Mechanisms of Dreaming." Electroenceph Clin Neurophysiol. [1963]: Supplement 24.). Jouvet also found that the subcortical structures of these test animals with this brain preparation continued to experience normal sleep/wake neural cycles. Jouvet’s studies suggest that cortical activation is nonexistent in the absences of a neural connection to subcortical structure. This is consistent with the idea that recent brain structures merely enhance the function of prior structures and are, therefore, dependent on these prior structures for functionality. When we combine these decorticate findings with results from studies involving the reticular activation system, we have a sense that nothing happens in the cortex without a subcortical neural directive.

Through the afferent neural hierarchy of the brainstem, we can see a succession of tactile sensory advancement—taste to sound detection to teeth and face sensory (myelencephalon to mesencelphalon)—arising before the afferent neural developments associated with visual sensory (Optic nerve). After the emergence of visual sensory, we find what looks very much like contemporary brain structure in miniature. The thalamus, with its right and left hemisphere and hemispheric adhesion, mirrors the design of cortical structure. The emergence of the thalamus after the emergence of visual perception in brain structure suggests sight’s contribution to what defines and quantifies the nature of mind.

Mind is the environment of cognitive activity within brain structure that arises from brain function. Through my investigation of thalamic evolution, I’ve determined that a mind is quantified by its capacity to integrate multiple sources of sensory afferents through a process that produces behaviors independent of instinct; i.e., a mind enables proactive rather than reactive behaviors. Before the emergence of sight sensory neural developments, behaviors were primarily reactive to tactile sources of sensory (touch, taste, and sound), which could not be distinguished before being physically perceived. With sight emergence, ancestral animals could integrate what they felt with what they saw to more effectively and efficiently mediate their behaviors. The thalamus is the most primitive structure in the contemporary brain where such divergent sensory integration occurs. The emergence of the thalamus after sight developments suggests that its function gave ancestral animals the rudiments of thought.

I have postulated that thalamic function is the scaffold around which mind is constructed. Couple this with the dependency of cortical function on subcortical neural inputs, mind cannot exist without thalamic function. Rather than the initiate of thought processes, cortical function merely assesses, attenuates, and stores subcortical directives and afferents. In my opinion, it is the thalamus that tells the cortex what to think and what to think about.

Another compelling piece of data that corroborates this idea is the fact that the greatest volume of projections reaching the cortex originate from the cortex itself, and not from other external structures. The cortex is deeply interconnected with itself.

I believe this deep interconnectivity is indicative of the human cortex’s superior ability to attenuate complex responses from limited subcortical directives and afferents. Human survival is uniquely dependent on its ability to attenuate complex mental, emotional, and behavioral responses, from minuscule sensory input, to compete effectively against equally perceptive members of its species. I’ve envisioned the dynamics between the human thalamus and cortex as a dullard wearing a “thinking cap”.

But of course there is evidence against this notion. I just learnt for instance that the cortico-thalamic connections in the cat's primary visual cortex outnumber the projections going in the other direction by a rate of 10:1. That is, there are more fibers sending information back to the thalamus than are fibers doing the opposite.

This may also support the idea of how cortical function attenuates complex responses (efferents) from limited subcortical afferents.

Approaching the problem from an evolutionary perspective, we get another interesting fact against my hypothesis. The only sense that bypasses the thalamus is the sense of smell. Olfactory information is sent directly to an "older" cortex, where smells are processed. This is relevant because evoking smells is infinitely harder than evoking images, concepts or emotions. In fact, a whole plethora of sensations are simulated in our dreams -- guess which one is very rare to appear? That's right, smells and odors. So this somewhat supports the notion that the thalamus might play a whole in this inner blackboard we have in our minds.

Indeed, smell sensory enters the paleocortex initially but arrives eventually in the dorsomedial nucleus of the thalamus for dispersal to olfactory associated cortical areas. However, the limited reports of smell imagery in dream content should not be attributed to the complexity of evoking, without a sensory source, smell associated memories.

A misperception of many sleep researchers is the idea that dreams are products of a memory associated “creative” process akin to daydreaming. This misperception, in part, is based on studies of activations in brain areas associated with memory and mental acuity tests in sleep deprivation studies. The reality is that dreaming is an interpretive process rather than a creative process. Amid sleep, the brain arouses to wakeful levels of activation as a consequence of vestigial metabolic activations and deactivations in the brainstem. Brainstem activations amid the sleep process arouse the cognitive centers of the brain that, when aroused, set about the task of interpreting the random neural activations associated with the metabolic processes of the brainstem. The images in our dreams, including smell, are interpretations of neural activations experienced by the brain amid the sleep process. Rather than the difficulty of conjuring scent imagery, scent imagery may not appear often in dream content because the quality scent interprets is frequently not among the neural afferents from the brainstem, which our dreaming brain perceives and interprets amid sleep. Whether smell occurs frequently in dream content is dependent on the mindset of the dreamer. Certainly, a baker or chef would have considerably more dreams of scent related imagery than would an acrobat by virtue of a mindset enveloped by a profession associated with food aroma. I welcome your further thoughts.