What is a Brain
From Lettvin
What is a brain?
A brain is a specialized subset of a colony of cells, that facilitates survival of entire colony by assessing risks and benefits from a distance. It does this by receiving, processing, and interpreting stimuli received from the sensorium, the sensory apparatus of the body.
The sense organs perceive changes (stimuli) that occur within the sensible environment, process the stimuli into signals to transmit to the brain.
The brain projects the signal activity over one or more layers into a discrete spatial topology within a volume this needs to be clearer. It collects the statistical model of the sensorium and likely outcomes from a discrete spatial topology this also needs clarification from that same volume then signals cells in the general community to change their actions or not.
What does a brain do?
Signals arriving at a sense organ are temporo-spatial, that is they bring in information about changes that occur in time and space. A retina senses a diffraction pattern over a community of individual receptors. Skin senses patterns of pressure, temperature, and more. In fact, all senses work by community evaluation of changes in waves called features.
To borrow from electronics engineering, a receptor's response consists of two components. A DC component measures ambient wave pressure; an AC component measures changes in that pressure. The DC component provides a feedback signal to scale and cancel unchanging input. The AC component is a feed-forward signal to indicate a change in input in proportion to the DC component. At extremes of receptor function, this proportionality is reduced. Receptors have mechanisms to extend their range to prevent this reduction.
How does a brain do it?
Feedback from an individual sensor within a sense organ or one of its neighbors, sometimes distant neighbors, may attenuate or cancel the sensor's output. In other cases, this attenuation is delivered from predictions made by deeper layers. In all cases, the role of the brain is to cancel all the signal it can by comparison with neighbors and prediction. What remains is a difference signal.
Difference signals identify the "primitive sketch" of objects in the sensorium. Layer by layer, uncanceled differences propagate deeper until a reflex cancellation feedback is generated. At that layer, the difference signal stops and no signal proceeds deeper. A brain that predicts from a deeper layer uses the lack of signal as an indicator of successful prediction. It tests this by occasional cessation of prediction to sense otherwise canceled signal.
A primitive sketch comprises a double-sided boundary between different regions. The primitive sketch is all the information needed by a brain. Regions of identical sense data generate no difference signal. This dramatically reduces the data flow by approximately 1 dimension. For instance, a 2D image reduces to a double-sided 1D line bounding objects in the image.
