Hardware and software of the brain - страница 3
Fig. 5. Coronal cut of anterior section of the Brain showing basal ganglia.
Finally, anatomy names a complex which is defined not by proximity or similarity of its parts, but by strong connections between them.
Fig. 6. Schematic briefly summarizing neural systems proposed to process emotion, highlighting structures that are visible on the medial surface of the brain. Papez's (1937) original circuit (A) was expanded upon in the concept of the limbic system (B) to include a variety of subcortical and cortical territories (MacLean, 1952; Heimer and Van Hoesen, 2006).
This is the limbic system. Its components are located in the midbrain and forebrain.
Hardware
Computers are made of electronic components which were also known as radio details because before the advent of microprocessors computers were made of the same details as radio, TV, and other consumer electronics. Elementary components of the brain are neurons – specialized nerve cells which can generate electric pulses and conduct them to long distances of tens of centimetres. There are different types of radio details: resistors, capacitors, transistors, and a few others. Likewise, there are a few (of the order of 10) different types of neurons which may be repeatedly encountered in the different parts of the nervous system. The most substantial difference between them is that some are excitatory, others – inhibitory. That is, firing of the first neuron may force the second to fire too, or suppress its background firing rate instead. Neurons are not the only cells of the brain. There is also glia (which serves as damper for neurons and insulator for long wires – nerves) and blood vessels which are indeed a special type of muscles.
Computer is a device that processes information. How is information represented in the brain? We can't determine immediately how our ideas are represented, but we can draw conclusions watching what happens when they come out to periphery and convert themselves into physical actions. It was definitely established that muscular tension depends upon the average firing rate in the nerve that ends up on this muscle. Hence, we can suppose that a single spike of a single neuron in the central nervous system doesn't matter and our ideas are encoded by the pulse activity averaged over a group of adjacent cells (called a cluster) and a certain period of time. The typical number of elements in such clusters is of the order of 1000. As to time parameters, the duration of one spike is approximately 1 millisecond so the firing rate of 1 neuron can't be more than 1 kilohertz. Multiplying it by the number of elements in the cluster, we get 1 megahertz, but keep in mind that the reaction time still can't be less than 1 millisecond because spikes are not rectangular.