About the Brain

A typical human brain is 17 cm from front to back and contains between 50 and 100 compartments. It is topologically organized.

The cerebellum is involved with the coordination of simultaneous muscle movements. It cannot initiate any activity by itself, but acts as a helper to the motor cortex. There are five different types of neurons in the cerebellar cortex: Purkinje, granule, Golgi, basket, and stellate cells. They are arranged with stereotyped precision. Granule cell axons are called parallel fibers; their junctions with Purkinje cell dendrites may be modifiable as the cerebellum learns a particular skill.

Brain signals (EEGs) can be picked up by electrodes making contact with the scalp. Only activity in the immediate vicinity of the electrode is detected. In an awake person the EEG is due to slowly propagating graded potentials. If the person's eyes are closed, alpha oscillations are picked up, especially from an electrode at the back of the head. It is conjectured that the alpha rhythm is due to a visual feedback loop that goes into oscillations because gain is increased. During deep sleep the EEG displays slow waves of large amplitude, probably as neurons are rejuvenated.

Any change in the brain that represents memory is called an engram. The modern view is that the basis for memory is synaptic junction modification, and that engrams are stored in the same part of the brain that recognizes that particular type of pattern.

A block diagram attempt to summarize the mechanisms of memory is presented. As far as time is concerned, there is extremely-short-term, shortterm, and long-term memory. There are two categories of stored information: procedural and declarative. Damage to certain central structures in the brain can result in anterograde or retrograde declarative amnesia, or various degrees of both.

The block diagram of a hypothetical simple brain is presented. A ?>central station?> box is the ?>seat of consciousness.?> Each sensory receptor leads to a ?>feature extraction?> box. Important patterns are stored in ?>pattern memory stacks,?> with association fibers running between the various stacks. A ?>thought pattern memory stack?> circulates association fiber signals over and over again. Because of a random noise generator, the robot is somewhat unpredictable, and sometimes comes up with a new idea.

The determinism versus free-will controversy is reviewed. Laplacian determinism should be modified because it is impossible for us to predict the future of a single neuron, let alone 10¹² of them. Besides, prediction requires precise measurements that violate quantum mechanics.

Consciousness is defined as an awareness of one's own existence, sensations, thoughts, and environment. It is a mysterious attribute of the brain that is undoubtedly shared by all mammals. Since honey bees are capable of a great deal of learning, perhaps they (and insects in general) also have an awareness of being.