Human Brain evolution

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Gary Lynch & Richard Granger

Big Brain: The Origins and Future of Human Intelligence. (2008)




6. From Olfaction to Cognition

The striatum, amygdala, hippocampus and thalamus are area of the brain with "different circuit structure" of the neurons that tie the prefrontal cortex to the hindbrain–or primary motor area from the brainstem to the limbs. These four significant parts of the central nervous system expanded from reptilian to mammalian species.


Striatum–"it is clearly involved in getting the body to move." (pp. 74-75.)

Amygdala–part of the forebrain–"sends massive connections to the hypothalamus, a set of regulatory structures that virtually runs the autonomic nervous systems of your body."


"The Amygdala largely rules the hypothalamus" ...."The hypothalamus operates your endocrine glands and generates simple primitive behaviors."

extreme rage, affection or 'raw emotions' states are triggered by electrical impulses to that region.

Hippocampus–"is central to the encoding of memory..." (generate epileptic seizures)--such that removal o of the hippocampus in severe epileptic seizure patients results in "marked memory deficit." That is patients are unable to form new memories when the hippocampus is damaged.

(pp. 77-78)

"It is noteworthy that the olfactory system sends its largest outputs to the hippocampus.

In simpler mammals (rodents) "in small brained mammals as a kind of higher-order processor of odor information."

p. 79.

Thalamo-cortical loops that tie the Thalamus to the pre-frontal cortex.

"as the brain grows large it becomes ever more important" . . . eventually becoming "the keystone of the brain."

p. 79.

"Striatum makes connections to frontal thalamo-cortical loops, just like the olfactory cortex does, thus creating even larger loops."

p. 80.

"Since the frontal cortex can control the striatum, it can use its burgeoning predictive abilities to refine the selection of what movements to perform in what situations. It thus becomes the beginning o of a system for planning."

p. 80.

"In particular, both the hippocampus an and the amygdala send their messages to the striatum, and the striatum inturn is linked,...back to other cortical and thalamo-cortical circuits."

p. 80.

"As a result every odor experience ends up sending not one but multiple messages to thalamo-cortical loops, one directly from the olfactory cortex, another via the striatum, and the rest via amygdala and hippocampus."

p. 80.

An architecture of the human mind
Interior switches  
pen in book

"...the connection from olfactory cortex to amygdala elicits autonomic and emotional responses . . .thirst, satiation, lust, sleepiness."

p. 81.

"The amygdala can determine both the intensity and the valence, good or bad, of the experience that the frontal cortex will eventually perceive."

"...the hippocampus is a crucial player in sorting these myriad experiences into a semblance of order.... Without the hippocampus, the animal will blow past a novel item, and new cortical memories will not be encoded."

That is stored for later use.
p. 82.


"Cues are recognized by a primary cortex which then in parallel distributes signals to regions that initiate movement (striatum), intensify or weaken the movements (amygdala), detect anomalies during the search (hippocampus) associate the cue with the object. (the hippocampus again), and organize actions in appropriate behavioral sequences (frontal-striatal-thalamo-cortical loops).

The other sensory systems–vision, audition, and touch–follow the same basic pathways in connecting the outside world to useful responses."

"The initial sensory cortical expansion was based on point to point organization, sending faithful representations of images and sounds forward into a neocortex that was set up...with random access network designs representative of the olfactory cortex."

The sensory-motor cortex areas of the brain.  

"That is, the switch from specialized mid-brain apparatus to cortical modes of processing allowed the brain for the first time to build multisensory unified representations of the external world."

"The result underlies the difference between the reptiles , largely lacking cross modal representations, and the mammals, possessing them."

p. 85.

"More or less evolved" is a widely, misunderstood term

"...a rat is in no sense less evolved than a monkey. Rodents are, in fact, a more recent order than primates, having emerged only after the mammals invaded the post dinosaur, day-time world."

Both advanced "point-to-point" designs and "random-access" organization and thus the associative and direct elements of the brain's architecture are indicative of all mammalian species.

"It is far more likely that the neocortex emerged using the ancient olfactory template, retaining its outputs to striatum, amygdala, and hippocampus, and that the specialized point-to-point sensory areas were filled in later, and modified independently.

"Yet again, we find evolution re-using an ancient adaptation for a novel purpose."

pp. 86-88.

See exaptation.

The brain's sensory cortex is a point-to-point represented here with the exaggerated size of the respective sensory-motor appendages in proportion to the number of nerve endings that are associated with these parts of the body. Hence the mind's eye view of the physical components of the organism may diverge from the actual proportions of each sensory-rich organ, appendage or sense gathering, body part.

The drawing is called the sensory-base "homunculus."

pen in book


"They determined that neurons in part of the rodents’ medial prefrontal cortex, an area of the brain involved in emotional processing in animals and people, had been firing often and rapidly in recent weeks, as had neurons in other, linked parts of the brain, including the amygdala, which is known to handle feelings of fear and anxiety."

"Why Exercise Makes Us Feel Good"
, New York Times, July 6, 2011, 12:01 am. 7-10-2011, Study on exercise and anxiety.

pen in book



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