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

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Abstract
Pattern-sensitive epileptics usually respond mainly to vertical or near-vertical gratings. Orientation selectivity was reexamined in 2 patients and the effects of hemifield stimulation are reported. Prior studies of subjects 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 conditions during the 1970 studies. With low-contrast gratings, Case 1 responded only to vertical orientations. 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. Orientation selectivity is apparently not a fixed property of the pattern-sensitive condition and 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. A functional difference between the upper and lower visual fields may exist.

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