Neuroendocrine system

General principles of structural and functional organization

The study of brain function has evolved from historical pseudoscientific theories to modern evidence-based concepts. At the end of the 18th century, F.J. Gall developed phrenology, the doctrine of determining a person's abilities from the contours of their skull. This theory was completely disproven.

Modern science rejects attempts to rigidly localize complex mental functions in specific areas of brain tissue. Complex mental activity is formed through multilevel connections between various regions. At the same time, there are highly specialized zones responsible exclusively for the primary analysis of sensory stimuli and direct movement regulation. The destruction of such zones leads to classical neurological symptoms: paralysis, blindness, hearing loss, aphasia, or coordination disorders. It is important to note that studying the brain structure of a healthy person (e.g., using MRI) provides no information about their personality traits or talents.

At the molecular level, regulation is provided by complex neurochemical pathways. For example, purines act as modulators for noradrenaline, acetylcholine, and GABA receptors. Knowledge of these mechanisms forms the basis for developing new safe psychotropic drugs.

Clinical presentation of frontal and parietal lobe lesions

Frontal lobe lesions radically alter the patient's personality and lead to cognitive decline. Motor activity drops, speech becomes stereotyped, or the patient becomes mute. The ability to analyze abstract concepts, plan actions, and predict their outcome is lost. Emotions are dominated by indifference, giving way to inappropriate euphoria.

• Medial regions: aspontaneity, a sharp decrease in motivation, deterioration of attention and memory come to the forefront.
• Basal regions: characterized by complacency, complete disinhibition, and anosognosia—lack of insight into one's condition and awareness of illness.
• Dominant hemisphere (area 44, Broca's center): motor aphasia develops.

Parietal lobe lesions vary depending on the side of the lesion. Damage to the dominant hemisphere causes dysgraphia, dyscalculia, and confusion between right and left sides. Pathology of the nondominant hemisphere is accompanied by impaired time perception, apraxia, and emotional restraint (dysphoria, hypomania). Extensive bilateral lesions lead to cognitive decline, inability to construct objects, impaired automated skills, and loss of tactile recognition of objects.

Pathology of the temporal and occipital regions

Temporal lobe damage impairs the comprehension of others' and one's own speech, as well as the recognition of sounds and music. Deep memory gaps are characteristic—fixation amnesia (Korsakoff's syndrome) occurs.

• Dominant hemisphere (area 22, Wernicke's center): manifests as sensory aphasia, auditory hallucinations, and euphoria.
• Bilateral lesion: Klüver-Bucy syndrome develops. Patients lose memory and intellect, become sexually disinhibited, and fail to recognize objects visually (compensating for the defect by feeling things or putting them in their mouths).
• Epileptic activity: provokes complex visual, olfactory, and auditory hallucinations. A sense of altered reality arises (derealization, déjà vu), along with surges of thoughts and twilight states of consciousness.

The occipital lobes are responsible for the primary recognition of visual information. Their loss causes blindness, hallucinations, and the inability to read and recognize faces. Irritation of this zone (by a tumor or epileptic focus) leads to elementary visual images (spots, flashes). Sometimes palinopsia is observed—the prolonged persistence of an object's image in consciousness after its disappearance.

Limbic system, hypothalamus, and asymmetry

Deep structures are inextricably linked with neuroendocrine functions and emotions.

1. Limbic system: includes the hippocampus, amygdala, thalamus, and mamillary bodies. Their damage causes increased sensitivity to pain, emotional disruptions, and fixation amnesia.
2. Hypothalamus: the central regulator. Its lesion disrupts body temperature, the sleep-wake cycle, appetite, and sexual behavior.
3. Reticular formation and locus coeruleus: these zones of the pons regulate the level of wakefulness and are also responsible for triggering fear and anxiety reactions.

The integration of these functions is based on brain asymmetry. The dominant hemisphere (left in most right-handers) controls speech, logical analysis, and thinking. The nondominant hemisphere is closely connected with the emotional sphere.

Class and exam questions

What else to study on this topic

• Clinical presentation of Klüver-Bucy syndrome
• Differential diagnosis of sensory and motor aphasia
• Specifics of basal and medial frontal lobe lesions
• The role of the hypothalamus in eating disorders and the sleep-wake cycle
• Functional asymmetry of the brain in psychiatric practice

Other topics in "Chapter 1. Biological Mechanisms of Human Behavior"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.