How does temporal lobe epilepsy impact cognition?
Temporal lobe epilepsy is the most common form of epilepsy. It is well studied and the deficits in temporal lobe epilepsy are well known. Seizures often begin in the hippocampus which is responsible for memory. If it begins in the dominant hippocampus, there will be verbal memory impairments and in the non-dominant hippocampus, visual spatial memory might be affected. The earlier the onside of temporal lobe epilepsy, the greater the memory impairment.
Then, not surprisingly in epilepsy populations, depression is a common co-morbidity. Depression and epilepsy together affect memory even more than if the person didn't have a co-existing depression.
Other cognitive deficits with temporal lobe epilepsy may include IQ, executive functioning and language. With dominant temporal lobe epilepsy, impaired naming is a common co-morbidity.
Another problem with temporal lobe epilepsy is that the earlier the onsite, particularly if the onset is in childhood or in infancy, the greater the likelihood of cerebral reorganization for language. Patients with early onset temporal lobe epilepsy of the dominant lobe tend to have atypical language distributions. They may either have bilateral language distribution or the language might shift entirely to the intact non-dominant side. This shift to the right hemisphere is associated with deficits of its own, particularly in non-verbal language. The organization's not considered to be extremely beneficial in temporal lobe epilepsy of early onset.
Cognitive disturbances in epilepsy are not static. They tend to get transiently worse after a seizure. A person who has a seizure can have a period of time called the “post ictal period”, which is characterized by the ending of the clinical seizure. The person is no longer shaking or trembling. However, the electrical activity continues to be impaired in the brain. During that post ictal period, there can be post ictal aphasias, particularly if the epilepsy is generated in the dominant temporal lobe.
Electrical disturbances can occur without clinical manifestations and they can cause transient impairments. The expectation is that the anti-epileptic drug will improve cognition by reducing the impact of the seizure. The AEDs will improve cognition because they lower these transient impairments. Therefore, the person should be able to recover cognitively sooner rather than later.
Rima Abou-Khalil received her Ph.D. from Vanderbilt University in 2003. She is currently a faculty member at Vanderbilt University with clinical and research interests in acquired neurogenic disorders.