Thalamus and Hypothalamus. From the point of view of studying the effects of drugs, the forebrain, which includes the thalamus, hypothalamus and some other structures, in particular, the cerebral cortex (see Fig. 3-5), is most important for us. The thalamus is often called a relay station, as it receives all the original impulses from the senses and transmits this information to the corresponding parts of the brain. The hypothalamus is the main organ regulating behavior. Obviously, its different parts are responsible for food, drink, body temperature, aggression and sexual behavior. To determine the exact purpose of a particular part of the brain is very difficult, and sometimes we get conflicting data. The main ways to study parts of the brain are damage and stimulation. In a surgical way, some part of the brain of the experimental animal is damaged. After the animal recovers from the operation,there are changes in his behavior that correlate with the damaged part of the brain. For example, damage to one part of the hypothalamus leads to the fact that the animal stops eating, and as a result of the operation in another area, the animal’s appetite is unnaturally increased, which even leads to obesity. Thus, we see that in the hypothalamus there are at least two areas responsible for eating: one regulates the feeling of fullness, the other – the feeling of hunger. Electrical stimulation of areas of the brain, as a rule, has the opposite effectwe see that in the hypothalamus there are at least two areas responsible for eating: one regulates the feeling of fullness, the other – the feeling of hunger. Electrical stimulation of areas of the brain, as a rule, has the opposite effectwe see that in the hypothalamus there are at least two areas responsible for eating: one regulates the feeling of fullness, the other – the feeling of hunger. Electrical stimulation of areas of the brain, as a rule, has the opposite effect damage.
Damage or stimulation of certain parts of the brain also extends beyond them, so that exposure can affect entire transmission channels of nerve impulses. Therefore, it is better to speak not about the centers of hunger, but about the channels of transmission of the corresponding impulses. However, even this approach can be simplified, because some researchers have noticed that not only information about hunger can be transmitted through such channels. So, they also affect the coordination of movements, taste sensations and much more. But be that as it may, all researchers agree that the hypothalamus plays an important role in controlling hunger, thirst, and other basic sensations.
The center of pleasure in the brain Despite these difficulties, electrical stimulation of brain areas was the basis of one of the most significant discoveries in research on the relationship between the brain, behavior and drugs. In the 1950s, psychologist James Olds worked with the brain of a rat, implanting electrodes in various parts of it and studying the effects of their stimulation. When electrically stimulating certain parts of the brain, the rat seemed to have fun. Here’s how Olds describes his discovery:
When the animal entered a certain corner of the cage, I gave him a short discharge of electric current. But the animal did not run away from the corner, but on the contrary, returned there after a short retreat caused by shock from the first stimulation. After the second stimulation, the retreat period was even shorter. By the time of the third electrical discharge, the rat did not go out of the corner.
Conducting further research, Olds and his colleague Milner found that if the electrodes were implanted in certain areas of the brain, especially in the middle forebrain, the rat could even be trained to press a lever in the cell, including electrocution, some neurons of the middle node go beyond its limits and connect it with the lateral part of the hypothalamus. When the rats learned to stimulate this area, they pressed the lever up to a thousand times per hour. This gave reason to assume that the “pleasure center” is being stimulated. Obviously, this part of the brain is the end point of the channels through which information about the desire for pleasure and its reception passes. Accordingly, to understand the properties of drugs to cause a sense of pleasure, it is necessary to study this area of the brain.One of the main channels of transmission of nerve impulses in the median node is dopamine, so the researchers put forward a version that the main chemical substance associated with the property of drugs to bring pleasure is dopamine. This is supported by the success of the next experiment. The rats learned to press a lever that delivers cocaine through a miniature pipette implanted in the median forebrain. Thus, people who use cocaine, change the chemical processes occurring in the system of control over pleasure.implanted in the median forebrain node. Thus, people who use cocaine, change the chemical processes occurring in the system of control over pleasure.implanted in the median forebrain node. Thus, people who use cocaine, change the chemical processes occurring in the system of control over pleasure.
The structure of the forebrain includes three more complex organs: the limbic system, the basal ganglia and the cerebral cortex. These bodies form such inherent only to man areas of mental activity, such as memory, logic, speech, planning and reasoning.
Limbic system. These are several organs located inside the forebrain. One of them, amidal, is responsible for certain types of aggression. Another important organ of the limbic system is the hippocampus (seahorse), an important part of the memory system. People with a damaged hippocampus will remember everything that happened to them before the damage, but they are unable to remember new information. Alcohol abuse in combination with poor nutrition leads to a serious mental disorder, known as Korsakov syndrome. In patients suffering from this disease (usually alcoholics from the lower classes of society), there is a memory disorder that is associated with damage to the hippocampus.
Ganglion. One of the causes of Parkinson’s disease is damage to the ganglion, namely the degeneration of a special group of nerve cells, the so-called “black substance”. These cells produce dopamine for the ganglion, and with their degeneration, less and less dopamine is involved in the transmission of nerve impulses. Interestingly, Parkinson’s disease does not occur as long as at least 20% of the substantia nigra cells remain intact.
Cortex. In fig. 3-4 shows the lobes of the cerebral cortex. The occipital lobe is associated with vision and perceives signals from the optic nerve. The temporal lobe plays an important role in the processing of auditory sensations and, apparently, controls the mechanisms of speech. Damage to the left temporal lobe causes a serious impairment of speech ability (at least if the person is right-handed). Damage to the right temporal lobe often affects emotional reactions. In left-handers, the right temporal lobe is responsible for speech, and the left – for emotions. The frontal lobe controls movements and balance, as well as is connected with the emotional and mental sphere and personal characteristics of the character. The parietal lobe analyzes impulses from the organs of touch.