Искажённая карта тела в коре головного мозга (Искажённая соматотопическая карта)

Distorted model of the body corresponding to sensory and motor nerve density

A cortical homunculus is a distorted representation of the human body, based on a neurological "map" of the areas and proportions of the human brain dedicated to processing motor functions, and/ or sensory functions, for different parts of the body. Nerve fibresconducting somatosensory information from all over the bodyterminate in various areas of the parietal lobe in the cerebral cortex, forming a representational map of the body. Findings from the 2010s and early 2020s began to call this interpretation into question, and research is ongoing in this field.

A motor homunculus represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body. The primary motor cortex is located in the precentral gyrus, and handles signals coming from the premotor area of the frontal lobes. A sensory homunculus represents a map of brain areas dedicated to sensory processing for different anatomical divisions of the body. The primary sensory cortex is located in the postcentral gyrus, and handles signals coming from the thalamus. The amount of cortex devoted to any given body region is not proportional to that body region's surface area or volume, but rather to how richly innervated that region is. Areas of the body with more complex and/or more numerous sensory or motor connections are represented as larger in the homunculus, while those with less complex and/or less numerous connections are represented as smaller. The resulting image is that of a distorted human body, with disproportionately huge hands, lips, and face. In the sensory homunculus, below the areas handling sensation for the teeth, gums, jaw, tongue, and pharynx lies an area for intra abdominal sensation. At the very top end of the primary sensory cortex, beyond the area for the toes, it has traditionally been believed that the sensory neural networks for the genitals occur. However, more recent research has suggested that there may be two different cortical areas for the genitals, possibly differentiated by one dealing with erogenous stimulation and the other dealing with non erogenous stimulation.

Wilder Penfield and his co investigators Edwin Boldrey and Theodore Rasmussen are considered to be the originators of the sensory and motor homunculi. They were not the first scientists to attempt to objectify human brain function by means of a homunculus. More recent studies have improved this understanding of somatotopic arrangement using techniques such as functional magnetic resonance imaging (fMRI).

Penfield referred to his creations as "grotesque creatures" due to their strange looking proportions. For example, the sensory nerves arriving from the hands terminate over large areas of the brain, resulting in the hands of the homunculus being correspondingly large. In contrast, the nerves emanating from the torso or arms cover a much smaller area, thus the torso and arms of the homunculus look comparatively small and weak. Penfield's homunculi are usually shown as 2 D diagrams. This is an oversimplification, as it cannot fully show the data set Penfield collected from his brain surgery patients. Rather than the sharp delineation between different body areas shown in the drawings, there is actually significant overlap between neighboring regions. The simplification suggests that lesions of the motor cortex will give rise to specific deficits in specific muscles. However, this is a misconception, as lesions produce deficits in groups of synergistic muscles. This finding suggests that the motor cortex functions in terms of overall movements as coordinated groups of individual motions. The sensorimotor homunculi can also be represented as 3 D figures (such as the sensory homunculus sculpted by Sharon Price James shown from different angles below), which can make it easier for laymen to understand the ratios between the levels of motor or sensory innervation of different body regions. However, these 3 D models do not illustrate which areas of the brain are associated with which parts of the body. In a 2021 article by Haven Wright and Preston Foerder published in the peer reviewed journal Leonardo entitled "The Missing Female Homunculus", the authors revisit the history of the homunculus, shed light on current research in neuroscience on the female brain, and reveal what they believe to be the first sculpture of the female homunculus, done by the artist and first author Haven Wright, based on the current research available.