History’s Top Brain Computation Insights: Day 14

Neuron staining illustrating column structure in cortex14) Neocortex is composed of columnar functional units (Mountcastle – 1957, Hubel & Wiesel – 1962)

Mountcastle found that nearby neurons in monkey somatosensory cortex tend to activate for similar sensory experiences. For example, a neuron might respond best to a vibration of the right index finger tip, while a neuron slightly deeper in might respond best to a vibration of the middle of that finger.

The neurons with these similar 'receptive fields' are organized vertically in cortical columns. Mountcastle distinguished between mini-columns, the basic functional unit of cortex, and hyper-columns, which are functional aggregates of about 100 mini-columns.

Hubel & Wiesel expanded Mountcastle's findings to visual cortex, discovering mini-columns showing line orientation selectivity and hyper-columns showing ocular dominance (i.e., receptive fields for one eye and not the other). The figure below illustrates a typical spatial organization of orientation columns in occipital cortex (viewed from above), along with the line orientations corresponding to each color patch.

Implication: The mind, largely governed by reward-seeking behavior, is implemented in an electro-chemical organ with distributed and modular function consisting of excitatory and inhibitory neurons communicating via ion-induced action potentials over convergent and divergent synaptic connections strengthened by correlated activity. The cortex, a part of that organ composed of functional column units whose spatial dedication determines representational resolution, is involved in perception (e.g., touch: parietal lobe, vision: occipital lobe), action (e.g., frontal lobe), and memory (e.g., temporal lobe).

Orientation selective cortical columns 

[This post is part of a series chronicling history's top brain computation insights (see the first of the series for a detailed description). See the history category archive to see all of the entries.]

-MC

One Response to “History’s Top Brain Computation Insights: Day 14”

  1. Cogito Conversation: Dr. Tilak Ratnanather, Brain Mapper | Cogito Says:

    [...] area if you believe the cortical column model of the cortex. As you know Mountcastle developed his famous multicolumn model of the visual cortex, where neurons with similar ‘receptive fields’ are organized vertically in cortical [...]

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