The dorsal lateral geniculate nucleus (dLGN) in carnivores and primates is a laminated structure, where each layer gets visual input from only one eye [1, 2]. By contrast, in rodents such as mice and rats, the dLGN is not overtly laminated, the retinal terminals from the two eyes are only partially segregated [3, 4], and many cells in the binocular segment of dLGN get excitatory inputs from both eyes [5, 6]. Here, we show that the evolutionary ancient koniocellular (K) division of primate dLGN, like rodent dLGN, forms a subcortical site of binocular integration. We recorded single-cell activity in dLGN of anesthetized marmoset monkeys. As expected, cells in the parvocellular (P) and magnocellular (M) layers received monocular excitatory inputs. By contrast, many cells in the K layers received excitatory inputs from both eyes. The specialized properties of distinct K sub-populations (for example, blue-yellow color selectivity) were preserved across the two eye inputs, and where tested, the contrast sensitivity of each eye input was roughly matched. The results argue that evolutionarily widely separated orders such as rodents and primates have a shared strategy of integrating signals from the two eyes in subcortical circuits.

Romo PA, Wang C, Zeater N, Solomon SG, Dreher B. Phase sensitivities, excitatory summation fields, and silent suppressive receptive fields of single neurons in the parastriate cortex of the cat. J Neurophysiol 106: 1688 -1712, 2011. First published June 29, 2011 doi:10.1152/jn.00894.2010We have recorded single-neuron activity from cytoarchitectonic area 18 of anesthetized (0.4 -0.7% isoflurane in 65% N 2 O-35% O 2 gaseous mixture) domestic cats. Neurons were identified as simple or complex on the basis of the ratios between the phase-variant (F1) component and the mean firing rate (F0) of spike responses to optimized (orientation, direction, spatial and temporal frequencies, size) high-contrast, luminance-modulated, sinewave drifting gratings (simple: F1/F0 spike-response ratios Ͼ 1; complex: F1/F0 spike-response ratios Ͻ 1). The predominance (ϳ80%) of simple cells among the neurons recorded from the principal thalamorecipient layers supports the idea that most simple cells in area 18 might constitute a putative early stage in the visual information processing. Apart from the "spike-generating" regions (the classical receptive fields, CRFs), the receptive fields of threequarters of area 18 neurons contain silent, extraclassical suppressive regions (ECRFs). The spatial extent of summation areas of excitatory responses was negatively correlated with the strength of the ECRFinduced suppression of spike responses. Lowering the stimulus contrast resulted in an expansion of the summation areas of excitatory responses accompanied by a reduction in the strength of the ECRFinduced suppression. The spatial and temporal frequency and orientation tunings of the ECRFs were much broader than those of the CRFs. Hence, the ECRFs of area 18 neurons appear to be largely "inherited" from their dorsal thalamic inputs. In most area 18 cells, costimulation of CRFs and ECRFs resulted in significant increases in F1/F0 spike-response ratios, and thus there was a contextually modulated functional continuum between the simple and complex cells. luminance-modulated gratings; simple and complex cells; spatial and temporal properties; classical and extraclassical receptive fields; primary visual cortex HUBEL AND WIESEL (1965) postulated that in the domestic cat, the so-called parastriate cortex (cytoarchitectonic area 18 of Gurewitsch and Chatschaturian 1928; cf. Otsuka and Hässler 1962) constitutes a "higher order" visual cortical area (Fig.

The koniocellular (K) layers of the primate dorsal lateral geniculate nucleus house a variety of visual receptive field types, not all of which have been fully characterized. Here we made single-cell recordings targeted to the K layers of diurnal New World monkeys (marmosets). A subset of recorded cells was excited by both increments and decrements of light intensity (on/off-cells). Histological reconstruction of the location of these cells confirmed that they are segregated to K layers; we therefore refer to these cells as K-on/off cells. The K-on/off cells show high contrast sensitivity, strong bandpass spatial frequency tuning, and their response magnitude is strongly reduced by stimuli larger than the excitatory receptive field (silent suppressive surrounds). Stationary counterphase gratings evoke unmodulated spike rate increases or frequency-doubled responses in K-on/off cells; such responses are largely independent of grating spatial phase. The K-on/off cells are not orientation or direction selective. Some (but not all) properties of K-on/off cells are consistent with those of local-edge-detector/impressed-by-contrast cells reported in studies of cat retina and geniculate, and broad-thorny ganglion cells recorded in macaque monkey retina. The receptive field properties of K-on/off cells and their preferential location in the ventral K layers (K1 and K2) make them good candidates for the direct projection from geniculate to extrastriate cortical area MT/V5. If so, they could contribute to visual information processing in the dorsal ("where" or "action") visual stream.We characterize cells in an evolutionary ancient part of the visual pathway in primates. The cells are located in the lateral geniculate nucleus(themainvisualafferentrelaynucleus),inregionscalledkoniocellularlayersthatareknowntoprojecttoextrastriatevisualareas as well as primary visual cortex. The cells show high contrast sensitivity and rapid, transient responses to light onset and offset. Their properties suggest they could contribute to visual processing in the dorsal ("where" or "action") visual stream.