Transient Inability to Distinguish Between Faces: Electrophysiologic Studies

Abstract

It is not known with certainty at which level of face processing by the cortex the distinction between a familiar and an unfamiliar face is made. Subdural electrodes were implanted under the fusiform gyrus of the right temporal lobe in a patient who developed an unusual inability to distinguish differences between faces as part of the epileptic aura ("all faces looked the same"). A cortical region located posterior to the epileptic focus was identified that exhibited a maximum evoked response to the presentation of facial images (N165), but not to objects, scenes, or character strings. Evoked potentials elicited by a variety of visual images indicated that any perturbation away from novel whole-face stimuli produced submaximal responses from this region of the right temporal lobe. Electrical stimulation of this region resulted in an impairment of face discrimination. It was found that presentation of familiar faces (grandmother, treating physician) produced a different response from that observed for novel faces. These observations demonstrate that within 165 msec of face presentation, and before the conscious precept of face familiarity has formed, this cortical region has already begun to distinguish between a familiar and an unfamiliar face.

Separate Face and Body Selectivity on the Fusiform Gyrus

“…In keeping with previous evidence from intracranial recordings (Allison et al, 1994), stimulation studies (Puce et al, 1999;Mundel et al, 2003) and neuropsychological studies (Wada and Yamamoto, 2001), our finding that some regions in the ventral visual pathway are apparently strongly selective for a single class of visual stimuli would seem to argue against the idea that all regions in the ventral visual pathway participate in the representation of each object (Haxby et al, 2001). However, two caveats must be mentioned here.…”

Intracerebral electrical stimulation of a face-selective area in the right inferior occipital cortex impairs individual face discrimination

“…This observation goes beyond our previous report of impairment in recognizing famous faces during a previous implantation in the same region (Jonas et al, 2012) and other electrical stimulation studies reporting impairment in face vs. no face categorization (Chong et al, 2013, see also Afraz et al, 2006 for modulation of face categorization by electrical stimulation of the monkey infero-temporal cortex), impairment in face naming (Allison et al, 1994;Puce et al, 1999) or distortions of the physician's face following electrical stimulation of other faceselective regions (Parvizi et al, 2012;Vignal et al, 2000). More related to our observations, Mundel et al (2003) reported an epileptic patient who stated that "all faces look the same" following electrical brain stimulation of the right fusiform gyrus, suggesting impairment in individual face discrimination. However, the patient reported the same feeling during epileptic seizures, and individual face discrimination was not tested experimentally during electrical stimulation.…”

Focal electrical intracerebral stimulation of a face-sensitive area causes transient prosopagnosia

“…Here, the coordinates of the stimulated region, and most importantly the fMRI and electrophysiological mapping provide decisive evidence that the disrupted functional area is the right OFA. Second, in contrast to subdural grids as used in previous stimulation studies (Allison et al, 1994Puce et al, 1999;Mundel et al, 2003), the Stereo-EEG method (Talairach and Bancaud, 1973) relies on intra-cerebral electrodes which allow us to use low voltage-electrical currents resulting in a very focal effect (e.g., 10 mA in Allison et al (1994) and Puce et al (1999) for 1 to 1.8 mA in the present study). Supporting this claim, high frequency intracerebral stimulation at low voltage is thought to evoke experiential phenomena through the disruption of the neural function near the stimulating electrode (Halgren and Chauvel, 1993).…”