Functional Architecture of the Brain
by David D. Olmsted (Copyright - 2004, 2006. Free to use for personal and
Last Revised August 29, 2006
Basic Functional Parts
The brain is like a puzzle in that one cannot understand any one region completely
unless one understands how that region fits into the brain's overall functional
information processing architecture. The following information is presented without evidence for the
purpose of a quick introduction and thus it should be considered preliminary and tentative.
In the following representation of the basic brain in figure 1
all the adjacent regions can be assumed to be reciprocally connected. The arrows
show the dominant connections in the non-mammalian brain.
The Main Functional Areas of the Brain
The Hypothalamus is the core of the brain having spontaneously active neurons that
“animate” everything else. Other brain regions just layer on various contraints
to these basic animating signals.
The Reticular formation is a routing network that
routes the hypothalamic signals to the appropriate muscles via appropriate gating.
Simple operant conditioning circuits would be found here.
Later in evolution it sends signals up to the thalamus to affect attention.
The Thalamus (Diencephalon) seems
to have started out as a contra-indicator center and later became mostly an attention controller.
It does this by inhibiting brain circuits that are activated from other regions.
The Tectum (Optic Lobe) localizes interestng (innately defined for the most part) motions to the animal.
It sends its signals to the reticular formation where they are directed to the appropriate
motor generating centers in the brain stem or to the thalamus which tells the animal
where to focus its attention or whether it should duck and hide.
The Cerebellum is an
adaptive predictive (feedforward) control system. As such it modifies the motor
patterns generated in the brain stem and spinal cord.
The Neocortex (Cerebrum) allows
the animal represent knowledge for planning (later reasoning) and recall despite only detecting partial information.
It does so in a general to specific hierarchy with a unique 3 port neural circuit. Despite
its dominance in humans it also exists in fish and amphibians. The Hippocampus is an
old part of the cerbrum and defines the
relative spatial context and later in evolution the temporal context for this hierarchy.
The septum enhances or suppresses the hypothalamic signals (motivations) for
acquisition (approach) while the amygdala enhances or suppresses all hypothalamic
signals (motivations) for active avoidance (retreat) based upon the environmental
situation. Because of this the septum is often called the "pleasure center" while
the amygdala because of its opposite functioning is often called the "punishment
center". In humans electrical stimulation of the septum can produce a feeling
of pleasure while stimulation of the amygdala can produce feelings of fear.
Other animals if given the chance to self-stimulate the septal enhancement
circuit will often self-stimulate to the exclusion of all other activities.
The ADVR (anterior dorsal ventricular ridge) orders features along pre-defined parameters.
This is in contrast to the neocortex which orders features along a general to specific
hierarchy. After reptiles the evolution of the brain diverged. In birds the
ADVR became dominant over the neocortex while in mammals the neocortex became dominant
over the ADVR with the ADVR ultimately disappearing. The
ADVR - basal ganglia circuit is probably why birds are so good at mimicry. The basal
ganglia takes the ordered feature signals from both the ADVR and neocortex and routes
them to the appropriate action or perception. As such it is somewhat analogous in purpose to the
reticular formation. In primates even this function tends to be less needed as the
cortex is sophisticated enough to control actions directly.
Below in figure 2 are illustrations of some representative brain types (not to scale).
Notice that the cerebellum of the frog is even smaller than that of the codfish
indicating that the brain adapts itself to the ecological niche of the animal and
not to any supposed evolutionary hierarchy. The tectum is equivalent to the Optic
lobe shown below and Olf. is short for olfactory.
Some Brain Comparisons
and Carpenter, M.B. (1964)
Truax, R.C.and Carpenter, M.B. (1964) Strong and Elwyn's Human Neuroanatomy. Fifth edition.
Williams and Wilkins, Baltimore