Hierarchies of Recursion Loops

This sketch is intended to indicate that the neural network likely functions as a nested hierarchy of recursion loops operating at perhaps ~20 ms for visual sensory circuits, maybe ~50 ms in association cortex areas for perception, and perhaps >1 second for decision circuits in frontal cortex. Of course the neural network does not consist of discrete loops as shown in this sketch but instead contains many intersecting and overlapping loops. Interneuron networks interlacing projection neurons’ dendritic trees will contribute to network stability.

There is considerable evidence that the processing time required in each cortical area for useful computation is of the order of 20-30 ms. (Rolls & Treves; Neural Networks, 177)

These recursive computations can comprise to a complex system organized at multiple timescales. Slow rhythms involve very large numbers of cells that can be "heard" over a long distance, whereas localized fast oscillations involving only a small fraction of neurons may be conveyed only to a few partners. Power spectrum of the EEG is a straight line on a log-log plot, showing amplitude increasing as frequency decreases.  This inverse relationship is expressed as the "one over f" power spectrum (also called "pink" noise). (Buzsáki - Rhythms of the Brain, 119)

Recursive networks incorporate feedback loops to sustain iterative dynamical processes based on continuous update of network state. (Squire; Fundamental Neuroscience, 847)

Recursion — Looping design of iterative information processing implemented in neural networks. (Pinker; How the Mind Works, 125)

The binding principle made possible by reentry is repeated across many levels of brain organization, thereby leading to consciousness.  (Edelman; Universe of Consciousness, 107)

Sensation of consciousness lags (~500 milliseconds) the biological mechanisms of consciousness. (Damasio; Feeling of What Happens, 127)

Feelings occur over several seconds, two to twenty seconds being common. (Damasio; Looking for Spinoza, 112)

Conscious experience is associated with the activity of populations of neurons that are widely distributed in the thalamocortical system. The distributed groups of neurons must engage in strong and rapid reentrant interactions. (Edelman; Universe of Consciousness, 62)

Mutual reentrant interactions, for a brief time, link various neuronal groups in each map to those of others to form a functioning circuit. Neurons that yield such circuits fire more or less in phase with each other, or synchronously. (Edelman; Wider than the Sky, 44)

Small local neural assemblies will tend to operate asynchronously and be drawn into larger neural assemblies via the associative property of memory. Sparse but widespread neuronal assemblies drawn together by the associative property of memory mediate the Gestalt functionality of the brain's neuronal circuitry. These ever-changing, sparse but widespread neural assemblies form the dynamic core of consciousness.

 

 

Return to — Reentry and Recursion

Return to — Neural Network