Intra-cerebral electrical stimulation of a face-sensitive cortical area causes transient specific impairment in face recognition

Abstract

We report the first case of transient impairment in face recognition – prosopagnosia – induced by intra-cerebral electrical stimulation. The patient was a 32-year-old right-handed woman (KV) who has medically intractable right occipital epilepsy. She never complained of difficulties in face recognition and present with normal face recognition abilities. Intra-cerebral electrodes were implanted stereotactically to record seizures and to perform focal electrical stimulation in order to define epileptogenic and functional zones. During stimulations of right and left occipito-temporal contacts (biphasic pulse; 50 Hz train of 5 s; from 1 to 1.8 mA), she was asked to name previously correctly recognized famous faces, objects and scenes (Figure 1). Six of seven bipolar stimulations including one common contact (named O7; Figure 2) located within the right inferior occipital gyrus reproducibly induced transient prosopagnosia which completely recovered immediately upon termination of the stimulation. The patient reported a disturbance in perceiving the spatial relationship of facial elements and being unable to perceive the face as a whole. Stimulations at this site never produced visual distortions, deficit in object and scenes recognition or epileptic discharges. Stimulations of all other contacts and electrodes did not elicit prosopagnosia. The brain region of interest was mapped using fMRI and intra-cerebral ERPs by contrasting responses to pictures of faces and objects (Figure 2). The eloquent stimulation site O7 was located exactly within the right occipital face area (OFA). A N170 face-specific potential was also recorded at the stimulation site reinforcing the functional specificity of this area for face perception. We also found a N170 face-specific potential at an anterior site F6, located at the edge of the right FFA. However, its stimulation did not evoke any prosopagnosia. These findings provide evidences that the right OFA is necessary for normal face perception as part of a bilateral occipito-temporal network of face-sensitive areas.

Meeting abstract presented at VSS 2012