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NROC69H3 Lecture Notes - Striatum, Biological Neural Network, Visual Cortex

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Michael Inzlicht

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The human brain has about 100 millions of neurons and each of those neurons connect
with 1000-10,000 other neurons through synapses
Therefore, the brain contains about 100 quadrillion synapses and they can produce
incalculable number of neuronal ensembles or circuits
By looking at the monkey‟s visual cortex connections, we can conclude that the brain is
highly organized
All neurons are interconnected with each other
Levels of brain organization:
1. Behavioral system
2. Interregional system
3. Regional circuits
4. Neurons
5. Synapse
6. Molecule/ion channels
7. Genes
Every neuronal circuit is unique and they can be classified into certain types
These circuits can be found in different brain regions and across different species
System level of brain organization
Serial organization is when information flows sequentially through different brain
structures in series
Example: action potentials encoding from visual field to retina, to thalamus, to primary
visual cortex to visual association cortex
Parallel organization is when information is segregated into “channels” that transmit
neuronal information in parallel
Example: parallel becomes important in vision it is when brain divides what it sees in
four components: color, motion, shape, and depth. These are individually analyzed and
then compared to stored memories, which helps the brain identify what you are viewing.
Brain will then combine all of these information into the field of view that you see and
There‟s also parallel cortico-striatal-thalamic loops, which subserves motor, spatial,
visual and affective information processing
Hierarchical organization and independence is generally thought as the cortical regions
are assert a top-down control over “subcortical” structures

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However, it doesn‟t mean that the lower centers of the brain can‟t function independently
many behaviors that are habitual or automated do not require the engagement of
higher center of the brain
For example: “walking” has minimal input from higher centers and walking is mediated
by spinal reflexes and its automated, it is needed since it will free the brain to work for
other activities like **chewing gum while walking.
** Hierarchical can be seen in different brain regions but also in different neural
circuitries such as stritalnigralstriatal dopamine pathways as well as forming closed
striatonigralstriatal loops, projections from the shell of striatum ( major input of basal
ganglia) innervate areas of the ventral tegmental area that is turn project to the striatal
region adjacent to the shell, the core region. The core in turn projects to areas of the
substantia nigra which then sends a dopamine projection to the more dorsal parts of the
striatum. This way the ventral striatal regions influence more dorsal striatal regions via
spiraling SNS projections. Refer to the diagram
Topographic organization, which simply means that the sensory receptors located close
together as in the touch receptors in adjacent areas of skin projects to neurons in the
thalamus and cortex that are also physically close together
Example: Homonculus
1. The somatosensory cortex has a topographical representation of the whole body,
forming a somatotopic map of the body surface
2. Motor neuron controlling closely spaced muscles are located together in adjacent
areas of the motor cortex
3. The auditory cortex is organized as a tonotopic map where the neurons sensitive to
sequential frequencies of sounds are arranged in order
Circuit organization
One neuron excited and activates the next neuron

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Inhibitory neuron in the middle, inhibits the next neuron
attached, instead of exciting it
Convergence: many neurons come to one neuron or Divergence:
one neuron projects to many neurons
the lateral inhibitory neurons inhibits the lateral neurons
Excited neuron, excites the next neuron, the excites a
inhibitory neuron that inhibits the first excitory neuron from getting excited * common
Excitory neuron excites the next neuron and the post
neuron then excites the pre neuron
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