Abstracts

RATIONALE: Generalized tonic-clonic seizures are often considered to involve the whole brain homogeneously. However, partial seizures with secondary generalization may involve specific brain networks more intensely than others leading to selective deficits. To investigate this phenomenon, we performed single photon emission computed tomography (SPECT) perfusion imaging and neuropsychology testing in relation to electroconvulsive therapy (ECT)-induced seizures.
METHODS: We performed Tc-99m HMPAO SPECT injections at specific times relative to seizure initiation in patients receiving either bilateral or right unilateral ECT treatment for depression. Interictal injections were performed under the same anesthesia used in ECT. A two sample t-test model was used in SPM99 comparing ictal and interictal SPECT scans. Patients were grouped according to ECT type (bilateral or right unilateral) and time of injection relative to ECT stimulus (0s, +30s, or +60s). To test retrograde memory, specific items were presented to each patient immediately before ECT. Three objects were presented verbally and four faces were presented visually. Patients were tested for recall of these items four hours after ECT.
RESULTS: Both bilateral and right unilateral ECT produced generalized tonic-clonic seizures. Analysis of CBF changes at consecutive time points showed evidence of early maximal activity at the region of seizure onset in the anterior frontal and temporal lobes followed by later activity in regions of seizure propagation such as the parietal lobes.
Bilateral ECT produced symmetric CBF increases in the frontal and temporal lobes as well as the parietal cortex and the cerebellum. However, in right unilateral ECT, a greater activation of the right frontal lobe and a relative sparing of the left temporal lobe were observed. Interestingly, we found that verbal retrograde memory was significantly impaired in bilateral ECT patients, but not in unilateral ECT patients.
CONCLUSIONS: Although generalized tonic-clonic seizures involve widespread regions of the brain, our results suggest that focal regions are activated sequentially, reflecting seizure propagation. Additionally, the activation of frontal and parietal association cortex may explain the profound loss of consciousness seen in generalized tonic-clonic seizures while the sparing of the left temporal lobe seen in right unilateral patients could explain the less severe impairments in verbal retrograde memory we observed in this group.
[Supported by: Dana Foundation Clinical Hypotheses in Neuroscience Award.]