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Frontal lobe epilepsy (FLE) accounts for 15 to 25% of patients with focal epilepsy. [1] It is widely held that this condition is difficult to diagnose because clinical manifestations are diverse, [2-4] and surface EEG recordings during frontal seizures lack specificity. [5,6] Neuroimaging is also less helpful in frontal than in temporal lobe seizures. [7-9]
The cognitive functioning of subjects with FLE is poorly understood. Milner and others have documented deficits in spatial, nonspatial, and sensory delay tasks [10-15] in FLE subjects after surgical resections, as well as deficits in sorting and monitoring of external sequence of events. [16,17] Findings are similar in studies of subjects with frontal lobe lesions who do not have seizures, [18] but these studies do not discern whether the cognitive state of the preoperative FLE subject is also compromised. One preliminary report noted deficits in a broad array of ``frontal'' cognitive tasks in presurgical subjects with focal FLE. [19]
In the primate, the dorsolateral prefrontal cortex is involved in the short-term memorization of sensory stimuli, as indicated by studies after prefrontal lesions using delay tasks such as delayed response, delayed alternation, or delayed matching. [20-22] Therefore, the dorsolateral prefrontal cortex is considered an important part of the neural substrate for what is called active or working memory, [23] or what James [24] termed ``primary memory'' at the conscious level.
Electrophysiological studies have described the presence of ``memory cells'' in the dorsolateral prefrontal cortex. These neurons are activated in a sustained manner during the delay or memorization period of delay tasks [25-30] and presumably constitute the temporary store of working memory.
Neuropsychological evidence in humans and lower primates, which indicates that the prefrontal cortex is involved in working memory, largely derives from the use of spatial delay tasks--tasks that require memorization of spatially defined information to …
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