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Hippocampal sclerosis specific to the mesial temporal lobe, is the most common type of such tissue damage. [ 159 ] [ 160 ] It is not yet clear, however, whether the epilepsy is usually caused by hippocampal abnormalities or whether the hippocampus is damaged by cumulative effects of seizures. [ 161 ]
The medial temporal lobe structures are critical for long-term memory, and include the hippocampal formation, perirhinal cortex, parahippocampal, and entorhinal neocortical regions. [ 4 ] : 196 [ 5 ] The hippocampus is critical for memory formation, and the surrounding medial temporal cortex is currently theorized to be critical for memory storage.
The hippocampus is a five centimetre long ridge of gray matter tissue within the parahippocampal gyrus that can only be seen when the gyrus is opened up. [1] [2] The hippocampus is described in three regions, a head, body, and tail. The head is the expanded part near to the temporal lobe.
Hippocampal sclerosis is the most common brain abnormality in those with temporal lobe epilepsy. [16] Hippocampal sclerosis may occur in children under 2 years of age with 1 instance seen as early as 6 months. [17] About 70% of those evaluated for temporal lobe epilepsy surgery have hippocampal sclerosis.
A focal impaired awareness temporal lobe seizure occurs if a person becomes unaware during any part of the seizure. [10] Approximately 80% of seizures in the temporal lobe begin in the mesial temporal region, frequently starting in or around the hippocampus. The hippocampus, found in both temporal lobes, is essential for memory and learning. [12]
The hippocampal formation is a compound structure in the medial temporal lobe of the brain. It forms a c-shaped bulge on the floor of the inferior horn of the lateral ventricle . [ 1 ] Typically, the hippocampal formation is said to included the dentate gyrus , the hippocampus , and the subiculum . [ 2 ]
It is separated from the apex of the temporal lobe by a sulcus called the rhinal sulcus. [1] Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon. An important landmark that crosses the inferior surface of the uncus is the band of Giacomini or tail of the dentate gyrus. [2]
The temporal lobes are a region of the cerebral cortex that is located beneath the Sylvian fissure on both the left and right hemispheres of the brain. [14] Lobes in this cortex are more closely associated with memory and in particular autobiographical memory. [15] The temporal lobes are also concerned with recognition memory.