Pattern‐Sensitive Epilepsy. II: Effects of Pattern Orientation and Hemifield Stimulation

Summary: The majority of pattern–sensitive epileptics described in the literature have responded mainly to vertical or near‐vertical gratings. In this study, orientation selectivity was reexamined in two patients and the effects of hemifield stimulation are also reported. Prior studies of our subjects by Chatrian et al. (1970) revealed that Case 1 was sensitive to all orientations and that Case 2 was responsive to vertical or near‐vertical gratings only. Upon reexamination, Case 1 was distinctly less sensitive to oblique orientations and Case 2 was slightly responsive to horizontal gratings. At the time of testing, Case 1 was clinically improved and Case 2 was acutely worse compared to their conditions during the 1970 studies. With low‐contrast gratings, Case 1 responded only to vertical orientations. However, when presented with a checkerboard pattern, he responded only when the edges were diagonal and not when they were vertical and horizontal. Upper hemifield gratings were epileptogenic, whereas lower hemifield presentations were almost ineffective. Lateral hemifield presentation produced discharges mainly in the contralateral hemisphere. The results suggest that orientation selectivity is not a fixed property of the pattern‐sensitive condition. Instead, it is apparently influenced by clinical status and pattern properties. The checkerboard results suggest that the epileptogenic feature of the pattern is its Fourier fundamental component rather than individual lines and edges. The hemifield results may indicate a functional difference between the upper and lower visual fields.