The length-response properties of cells in the feline dorsal lateral geniculate nucleus.

1. In this report we have systematically examined the length-response properties of a large population of cells recorded in the cat dorsal lateral geniculate nucleus (dLGN). The responses of A laminae dLGN cells were assessed by the use of conventional single-unit extracellular recording techniques. The length preference of these cells was examined by plotting multihistogram length tuning curves to moving bars of light. Bar length was randomized in an interleaved fashion under computer control. The other stimulus parameters were standardized within the limits of those routinely used to assess the length preference of cortical cells. 2. The majority of cells (186/198), whose length-response properties are considered in detail in this report, exhibited strong centre-surround antagonism and a mean degree of length tuning equivalent to, or exceeding, that seen in most cortical hypercomplex cells (71 +/- 1.18%, S.E.M., n = 186). 3. The values for X cells (74 +/- 1.41%, S.E.M., n = 100) and Y cells (67 +/- 2.13%, S.E.M., n = 74) were very similar, as were those of the on-centre (71 +/- 1.51%, S.E.M., n = 123) and off-centre (71 +/- 1.85%, S.E.M., n = 63) subgroups. 4. A distinct subgroup of the Y cell population was identified. These comprised the remaining twelve out of the 198 cells examined and their response properties were sufficiently distinct to merit classification as a discrete subpopulation of cells which we have termed nlY cells. They were characterized by very poor levels of both centre-surround antagonism and length tuning, and were most frequently encountered close to laminar borders. Their response properties have been described in detail elsewhere. 5. We quantitatively compared the degree of length tuning seen with moving bars to the strength of centre-surround antagonism assessed with flashing spots. The degree of length tuning did not necessarily follow the level of centre-surround antagonism. 6. Examination of the effects of unilaterally extending bar length to one or other side of the receptive field did not reveal the type of asymmetry frequently seen in cortical hypercomplex cells. 7. The high degree of length tuning seen in this study underlines the potential importance of geniculate response properties to the generation of the length-response properties of cortical hypercomplex cells. The findings are discussed in relation to the synaptic mechanisms contributing to the generation of length tuning at subcortical and cortical levels.