Fig. 10.4 ). In addition, the hippocampus and amygdala are connected to the prefrontal cortex, the basal forebrain, and the anterior cingulate cortex.
Bilateral temporal lobe lesions can produce Klüver-Bucy syndrome, which is characterized by loss of the ability to recognize the meaning of objects from visual cues (visual agnosia); a tendency to examine all objects, even dangerous ones, orally; attention to irrelevant stimuli; hypersexuality; a change in dietary habits; and decreased emotionality.
Although this syndrome was originally described as following large lesions of most or all of the temporal lobe, more recent studies have highlighted the role of the amygdala. The amygdala conditions the association of fear with painful stimuli and may trigger, via connections to the medial frontal cortex and anterior cingulate gyrus, emotional or avoidance responses when these stimuli recur. In addition, the amygdala projects to the nucleus accumbens, a region of the basal ganglia which has been called a “reward center.” The nucleus accumbens signals pleasurable events in response to dopaminergic input from the ventral tegmental area of the brainstem and is also the most common site of the plaques and tangles associated with Alzheimer’s disease.
Thefunctionsofthedifferentlobesofthecerebralcortexhavebeendefinedaccordingtoboththeeffectsoflesionsproducedbydiseaseorthoseofsurgicalinterventionstotreatdiseaseinhumansandfromexperimentsonanimals.Inanotherapproach,thephysicalmanifestationsofepileptic seizures havebeencorrelatedwiththebrainlocationsthatgiverisetoseizures(epileptic seizure foci). Forexample,epilepticfociinthemotorcortexcausemovementsonthecontralateralside;theexactmovementsrelatetothesomatotopiclocationoftheseizurefocus.Seizuresthatoriginateinthesomatosensorycortexcauseanepileptic aura inwhichatouchsensationisperceived.Similarly,seizuresthatstartinthevisualcortexcauseavisualaura(scintillations,colors),thoseintheauditorycortexcauseanauditoryaura(humming,buzzing,ringing),andthoseinthevestibularcortexcauseasensationofspinning.Complexbehaviorresultsfromseizuresthatoriginateintheassociationareasofthetemporallobe;inaddition,amalodorousauramaybeperceivediftheolfactorycortexisinvolved (uncinate fit).
The Electrical Activity of the Cortex