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In
neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...
, the superior frontal gyrus (SFG, also marginal gyrus) is a
gyrus In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ...
– a ridge on the brain's
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
– which makes up about one third of the
frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove betwe ...
. It is bounded laterally by the
superior frontal sulcus The superior frontal sulcus is a sulcus between the superior frontal gyrus and the middle frontal gyrus. See also * Inferior frontal sulcus The inferior frontal sulcus is a sulcus between the middle frontal gyrus and the inferior frontal gyrus ...
. The superior frontal gyrus is one of the
frontal gyri The frontal gyri are four gyri of the frontal lobe in the brain. These are four horizontally oriented, parallel convolutions, of the frontal lobe. The other main gyrus of the frontal lobe is the precentral gyrus which is vertically oriented, and ...
.


Function


Self-awareness

In
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area ...
experiments, Goldberg ''et al.'' have found evidence that the superior frontal gyrus is involved in
self-awareness In philosophy of self, self-awareness is the experience of one's own personality or individuality. It is not to be confused with consciousness in the sense of qualia. While consciousness is being aware of one's environment and body and lifest ...
, in coordination with the action of the
sensory system The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved i ...
.


Laughter

In 1998, neurosurgeon Itzhak Fried described a 16-year-old female patient (referred to as "patient AK") who laughed when her SFG was stimulated with
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
during treatment for
epilepsy Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
. Electrical stimulation was applied to the cortical surface of AK's left frontal lobe while an attempt was made to locate the focus of her epileptic seizures (which were never accompanied by laughter). Fried identified a 2 cm by 2 cm area on the left SFG where stimulation produced laughter consistently (over several trials). AK reported that the laughter was accompanied by a sensation of merriment or mirth. AK gave a different explanation for the laughter each time, attributing it to an (unfunny) external stimulus. Thus, laughter was attributed to the picture she was asked to name (saying "the horse is funny"), or to the sentence she was asked to read, or to persons present in the room ("you guys are just so funny... standing around"). Increasing the level of stimulation current increased the duration and intensity of laughter. For example, at low currents only a
smile A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. Some smiles include a contraction of the muscles at the corner of the eyes, an action known as a Duchenne smile. Among humans, a smile expresses ...
was present, while at higher currents a louder, contagious laughter was induced. The laughter was also accompanied by the stopping of all activities involving speech or hand movements.


Additional images

File:Superior frontal gyrus animation small.gif, Position of superior frontal gyrus (shown in red) File:Gray725 superior frontal gyrus.png, Left cerebral hemisphere seen from above File:Gray726 superior frontal gyrus.png, Lateral surface of left cerebral hemisphere File:Gray727 superior frontal gyrus.png, Medial surface of left cerebral hemisphere File:Slide2HAN.JPG, Cerebrum. Lateral view. Deep dissection. Superior frontal gyrus labelled at top-left. File:Superior Frontal - DK ATLAS.png, Medial surface of right cerebral hemisphere. File:Superior frontal gyrus coronal sections.gif, Superior frontal gyrus highlighted in green on coronal T1 MRI images File:Superior frontal gyrus sagittal sections.gif, Superior frontal gyrus highlighted in green on sagittal T1 MRI images File:Superior frontal gyrus transversal sections.gif, Superior frontal gyrus highlighted in green on transversal T1 MRI images


References

{{Authority control Gyri Frontal lobe