Abstracts

Rationale: To further our understanding and awareness of the phenomena palinacousis. Palinacousis is an auditory illusion of perseveration or persistence of sound impressions for some time after the cessation of auditory stimulation. It has been debated as to whether it is an ictal or interictal phenomena. There are 24 cases in the literature to date. This is the first example of palinacousis elicited by electrical stimulation during brain mapping from both auditory and non-auditory stimuli.Methods: An epilepsy patient underwent a two stage intracranial electrode study to characterize his seizure focus for resective surgery. He had 2 grids placed over the right side of his brain (Figure1). During his brain mapping procedure the superior temporal gyrus (primary auditory cortex) was electrically stimulated while various external auditory as well as thought stimuli were presented (Figure2).Results: When electrodes GRID B23-24 were stimulated at low current the patient heard a familiar “Jewish prayer from a distance”. When stimulated with higher current, he heard the examiners voice echo “Normal and here we go” which was said right before stimulation. The patient noted that he heard the phrase echo in his left ear but not exactly in the examiners voice. The patient was then asked to very clearly think something without saying it prior to stimulation. The patient thought “clinical nurse manager” and then heard “clinical nurse manager” during stimulation, but not in his voice. Finally, at this electrode pair the patient said the word “Sinai” aloud right before stimulation and during stimulation he heard “Sinai” on the left but with a doppler effect going around his head and not in his voice. When electrodes GRID B31-32 were stimulated at low current the patient heard an echo of what he had said just prior to stimulation. Then at low current the examiner said “and again”. During stimulation the patient heard “again” but “fainter and in an accent..muffled”. At higher current the patient thought “elephant” and during stimulation heard the word “elephant” but not in his own voice. Stimulation of GRID B15-16 produced the sound of the fan in the room moving from right to left and intensifying. Stimulation of GRID B7-8 also produced the sound of the fan increasing in speed/ volume moving from left to right.Conclusions: The auditory cortex is in close proximity to the memory centers of our mesial temporal structures as well as to the complex integrative functioning of the insula. In the 1960’s Penfield and Perot stimulated the superior temporal gyrus and often elicited “flashbacks” consisting of sound and emotion from the patients past. In 1/520 patients stimulated the “operator’s voice echoed”. In 23 of the 24 previously described palinacousis cases an external source was identified as the perseverated stimuli. This is the first time a person’s thoughts were perseverated during electrical stimulation. Because palinacousis was in response to brain stimulation, this suggests that at least in some cases it is likely ictal. Echoing of ones own’s thoughts during stimulation suggests that hallucinations or even normal “ear worms” may arise from the auditory cortex.