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Chapter: Human Nervous System and Sensory Organs : Telencephalon

Neocortex: Temporal Lobe

Auditory Cortex, Functional Significance of the Temporal Cortex.

Temporal Lobe

Auditory Cortex

The main convolutions on the lateral sur-face of the temporal lobe run mostly longi-tudinally. However, two convolutions on the superior surface, thetransverse temporal gyri, or Heschl’s convolutions (C1), run trans-versely. They lie deep in the lateral sulcus and become visible upon removal of the overlying parietal operculum. The cortex of the anterior transverse convolution is the terminal station of the acoustic radiation  originating from the medial genicu-late body. The cortical areas of the two transverse convolutions correspond to area 41 (A) and area 42; they represent the audi-tory cortex. Like all receptive cortical areas,they are part of the koniocortex, or granularcortex. The external granular layer(II) and, even more so, the internal granular layer (IV) are rich in cells and very wide. The pyramidal layers (III and V), on the other hand, are narrow and contain only small pyramidal cells. The cortex of area 21 (B) is shown for comparison; it covers the medialtemporal gyrus and represents a typicaltemporal cortex with prominent granular layers, wide pyramidal layers, and distinct radial striation.

Electrical stimulation of area 22 close to the transverse convolutions induces acoustic sensations, such as humming, buzzing, and ringing. The auditory cortex is organized ac-cording to tone frequencies . In the human auditorycortex, the highest frequencies are assumed to be registered medially and the lowest frequencies laterally.

Functional Significance of the Temporal Cortex

Electrical stimulation of the remaining parts of the temporal lobe (performed during surgical treatment of temporal lobe epilepsy) induceshallucinations involving fragments of past experiences. The patients hear the voices of people familiar to them in their youth. They relive momentary episodes of their own past. These are mainly acoustic hallucinations and less often visual ones.

During stimulation of the temporal lobe, however, misinterpretation of the current situation may occur as well. A new situation may thus appear as an old experience (déjàvu). Surrounding objects may move away orcome closer. The entire surroundings may take on an uncanny or threatening character.


Such phenomena occur only upon stimulation of the temporal lobe and cannot be elic-ited from any other part of the cortex. It is therefore assumed that the temporal cortex plays a special role in the conscious and un-conscious availability of one ’s own past and of things experienced in the past. Only if we are continuously aware of past experiences are we able to judge and interpret new situations correctly. Without this ability, wewould not find our way around in our surroundings. Therefore, the temporal cortex has also been called the interpretative cortex.

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Human Nervous System and Sensory Organs : Telencephalon : Neocortex: Temporal Lobe |

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