Abstracts

RATIONALE: The left hippocampus is involved with learning acquisition, and verbal short-term memory (1). Left mesial temporal lobe epilepsy patients can present naming problems, verbal memory deficit and even acoustic-amnesic aphasia. This language disorder is characterized by memory retention of auditory-verbal traces deficit with inability to repeat 4 item word lists or large sentences, and morphological paraphasias (2). Deep brain stimulation of the hippocampus reduces seizures without impairing memory (3). Nevertheless, neither language nor cognitive function with voltage parameters changes has been studied. OBJECTIVE: Assess and measure naming and verbal memory before and after increasing of voltage parameters on temporal mesial lobe epilepsy patients with left hippocampal deep brain stimulation. METHODOLOGY: 4 patients with left hippocampal deep brain stimulation were included. Age 20-27; 3 M, 1F. Initial parameters: 3.5V, 450 msec pulsewidth, frequency 130 Hz, cyclic mode 1 min ON/4 min OFF. We did a clinic neuro-linguistic assessment in order to test fluency, comprehension, repetition and naming. In addition, we include two verbal memory tasks: word list and large sentences repetition as well a 100 picture naming test -50 Snoodgrass & Vanderwart (4) nouns & 50 IPNP (5) action verbs-. After the initial assessment we modified the amplitude parameters from 3.5V to 4.0V. After a 2 hours interval we did the post-test with the same methodology but different items, in order to avoid apathy and tiredness. RESULTS: No patient showed any significant deficit in language function at the pre condition (3.5V). With the voltage parameter increased to 4.0 V, 3 patients showed a non- significant increased in naming errors. One patient showed a 10% deficit in the picture naming test, compared to pre-condition and had 9 morphological paraphasias. As well, he could not repeat large sentences and needed some repetitions in comprehension assessment. In summary, diagnosis of one patient language deficit turns from mild disnomia (3.5V) in to an acoustic-amnesic aphasia (4.0V). The deficit was totally reversed when the voltage parameters were decreased. The patients who did not have any specific change on language function showed characteristic symptoms from parahippocampal stimulation so we can say that electrodes precise localization is crucial and these symptoms are very sensitive to small changes in voltage amplitude. CONCLUSIONS: Deep brain hippocampal stimulation is a good neurosurgical alternative for refractory epilepsy patients. However, fine changes in voltage amplitude could affect specific cognitive functions to go unnoticed in routine neurological assessment. This could affect the patient s life quality. On the other hand, this experiment contributes to study of the hippocampus key roll in language function.