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Cell types and response timings in the medial interlaminar nucleus and C-layers of the cat lateral geniculate nucleus
Published online by Cambridge University Press: 01 May 1999
Abstract
Previous evidence concerning the physiological cell classes in the medial interlaminar nucleus (MIN) has been conflicting. We reexamined the MIN using standard functional tests to distinguish X-, Y- and W-cells. Discharge patterns to flashing spots also were used to identify some cells as lagged or nonlagged, as previously done for the geniculate A-layers. Also, each cell's response timing (latency and absolute phase) was measured from discharges to a spot undergoing sinusoidal luminance modulation. Of 71 MIN cells, 48% were Y, 27% were W, 8% were X, and 17% were unclassifiable. Lagged and nonlagged discharge profiles were observed in each cell group, with 28% of all cells being lagged. Lagged cells displayed a response suppression and long latency to discharge following spot onset, and a slow decay in firing at spot offset that was often preceded by a transient discharge. These profiles were indistinguishable from those of lagged cells in the A-layers. MIN cells also were heterogeneous in response timing, displaying a range of latency and absolute phase values similar to that in the A-layers. We extended these analyses to 27 cells in the geniculate C-layers. In layer C, 35% of cells were Y, 10% were X, 25% were W, and 30% were unclassifiable. About 11% had lagged profiles, and were X-cells or unclassifiable cells. Layers C1 and C2 contained only W-cells and no lagged profiles. The range of timings in the C-layers was somewhat narrower than in the MIN. Overall, these results show that the MIN contains a greater variety of functional cell classes than heretofore appreciated. Further, it appears that mechanisms which create different timing delays in the A-layers also exist in the MIN and layer C. These timings may contribute to direction selectivity in extrastriate cortex.
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- 1999 Cambridge University Press
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