Frontal lobes of the brain

In the anterior part of each hemisphere of the brain is the frontal lobe (lobus frontalis). It ends in front with the frontal pole and is limited below by the lateral groove (sulcus lateralis; Sylvian groove), and behind by the deep central groove. The central groove (sulcus centralis; Rolandic groove) is located in the frontal plane. It begins in the upper part of the medial surface of the cerebral hemisphere, cuts across its upper edge, descends without interruption along the upper-lateral surface of the hemisphere downwards and ends slightly before reaching the lateral groove.

In front of the central sulcus, almost parallel to it, is the precentral sulcus (sulcus precentralis). It ends below, before reaching the lateral sulcus. The precentral sulcus is often interrupted in the middle part and consists of two independent sulci. From the precentral sulcus, the superior and inferior frontal sulci (sulci frontales superior et inferior) extend forward. They are located almost parallel to each other and divide the upper-lateral surface of the frontal lobe into convolutions. Between the central sulcus at the back and the precentral sulcus in front is the precentral gyrus (gyrus precentralis). Above the superior frontal sulcus lies the superior frontal gyrus (gyrus frontalis superior), occupying the upper part of the frontal lobe. Between the superior and inferior frontal sulci extends the middle frontal gyrus (gyrus frontalis medius).

Below the inferior frontal sulcus is the inferior frontal gyrus (gyrus frontalis inferior). Branches of the lateral sulcus protrude into this gyrus from below: the ascending branch (ramus ascendens) and the anterior branch (ramus anterior), which divide the lower part of the frontal lobe, hanging over the anterior part of the lateral sulcus, into three parts: opercular, triangular, and orbital. The opercular part (frontal operculum, pars opercularis, s. operculum frontale) is located between the ascending branch and the lower part of the precentral sulcus. This part of the frontal lobe received this name because it covers the insular lobe (islet) lying deep in the sulcus. The triangular part (pars triangularis) is located between the ascending branch at the back and the anterior branch at the front. The orbital part (pars orbitalis) lies below the anterior branch, continuing onto the lower surface of the frontal lobe. At this point, the lateral groove widens, which is why it is called the lateral fossa of the cerebrum (fossa lateralis cerebri).

The function of the frontal lobes is associated with the organization of voluntary movements, motor mechanisms of speech and writing, regulation of complex forms of behavior, and thought processes.

The afferent systems of the frontal lobe include deep sensitivity conductors (they end in the precentral gyrus) and numerous associative connections from all other lobes of the brain. The upper layers of cells of the frontal cortex are included in the work of the kinesthetic analyzer: they participate in the formation and regulation of complex motor acts.

Various efferent motor systems originate in the frontal lobes. In layer V of the precentral gyrus there are gigantopyramidal neurons that make up the corticospinal and corticonuclear tracts (pyramidal system). From the extensive extrapyramidal sections of the frontal lobes in the premotor zone of its cortex (mainly from cytoarchitectonic fields 6 and 8) and its medial surface (fields 7, 19) there are numerous conductors to the subcortical and brainstem formations (frontothalamic, frontopalpid, frontonigral, frontorubral, etc.). In the frontal lobes, in particular in their poles, the fronto-ponto-cerebellar tracts begin, which are included in the system of coordination of voluntary movements.

These anatomical and physiological features explain why, when the frontal lobes are damaged, mainly motor functions are impaired. In the sphere of higher nervous activity, the motor skills of the speech act and behavioral acts associated with the implementation of complex motor functions are also impaired.

The entire cortical surface of the frontal lobe is anatomically divided into three components: dorsolateral (convexital), medial (forming the interhemispheric fissure) and orbital (basal).

The anterior central gyrus contains motor projection areas for the muscles of the opposite side of the body (in the reverse order of their location on the body). The posterior part of the second frontal gyrus contains the "center" of turning the eyes and head in the opposite direction, and the posterior part of the inferior frontal gyrus contains Broca's area.

Electrophysiological studies have shown that neurons of the premotor cortex can respond to visual, auditory, somatic, olfactory and gustatory stimuli. The premotor area is capable of modifying motor activity due to its connections with the caudate nucleus. It also ensures the processes of sensorimotor relationships and directed attention. In modern neuropsychology, the frontal lobes are characterized as a block of programming, regulation and control of complex forms of activity.

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