8 October, 2007

How neural activity contains coded information

The electrically excitable cells in the nervous system that transport information, also called neurons, can produce short binary, all-or-nothing reaction-spikes of voltage, which travel as a pulse along the specialized extensions (axons) which causes the release of neurotransmitters. The spikes contain information about the world around the subject: what do I see, smell, hear, taste, feel, etc. But if also contains information about dilemmas of direction and assessment. Triggered spikes may mean different actions at different places and times in the brain. The rate of spiking in the central nervous system (brain and spinal cord) usually correlates with external properties, like color or an object. The peripheral nervous system has a different way of decoding spikes: more spikes correlate with more heat, louder sound or stronger muscle contraction.
When we go deeper in the brain, there are populations of neurons which are occupied with more complex, difficult to decrypt, properties, like reminiscence, judgments or desire.

The general idea nowadays is that mental information is not stored in single neuron-cells, but in populations of these cells and patterns of their activity. Current technology (for example inserting fine-electrodes directly in the brain) however is not equipped to measure several thousand neurons at once. Even one neuron is difficult to measure, for a simple neuron in the cortex may be connected with 10,000 other neurons.

Glial cells
Glial cells

Even though neuron-cells are the most studied, there may be other possibilities of informations transporters. For example glial-cells, which are poorly understood brain-cells that are 10 times as common as neurons. Other possibilities are different kinds of signaling mechanisms between cells involving gases and peptides, or biochemical processes located inside cells.

Humans, Neuroscience