Thalamocortical synapses in the cat visual system in vivo are weak and unreliable.

The thalamocortical synapse of the visual system has been central to our understanding of sensory computations in the cortex. Although we have a fair understanding of the functional properties of the pre and post-synaptic populations, little is known about their synaptic properties, particularly in vivo. We used simultaneous recordings in LGN and V1 in cat in vivo to characterize the dynamic properties of thalamocortical synaptic transmission in monosynaptically connected LGN-V1 neurons.

Inhibition in Simple Cell Receptive Fields Is Broad and OFF-Subregion Biased.

Inhibition in thalamorecipient layer 4 simple cells of primary visual cortex is believed to play important roles in establishing visual response properties and integrating visual inputs across their receptive fields (RFs). Simple cell RFs are characterized by nonoverlapping, spatially restricted subregions in which visual stimuli can either increase or decrease the firing rate of the cell, depending on contrast. Inhibition is believed to be triggered exclusively from visual stimulation of individual RF subregions.

Intracellular, , Dynamics of Thalamocortical Synapses in Visual Cortex.

Seminal studies of the thalamocortical circuit in the visual system of the cat have been central to our understanding of sensory encoding. However, thalamocortical synaptic properties remain poorly understood. We used paired recordings, in the lateral geniculate nucleus (LGN) and primary visual cortex (V1), to provide the first characterization of sensory-driven thalamocortical potentials in V1.

Synaptic mechanisms of temporal diversity in the lateral geniculate nucleus of the thalamus.

The lateral geniculate nucleus (LGN) contains a unique and numerous class of cells called lagged cells, which introduce a time delay into the neural signal provided to cortex. Previous studies have shown that this delay is dependent on GABA(A) receptors within the LGN. Furthermore, lagged cells have distinct integrative properties with a slower rising, more sustained, and overall lower firing rates than nonlagged cells.

Cellular mechanisms of temporal sensitivity in visual cortex neurons.

The ability of cortical neurons to accurately encode the temporal pattern of their inputs has important consequences for cortical function and perceptual acuity. Here we identify cellular mechanisms underlying the sensitivity of cortical neurons to the timing of sensory-evoked synaptic inputs. We find that temporally coincident inputs to layer 4 neurons in primary visual cortex evoke an increase in spike precision and supralinear spike summation.

Cellular mechanisms underlying stimulus-dependent gain modulation in primary visual cortex neurons in vivo.

Gain modulation is a widespread neuronal phenomenon that modifies response amplitude without changing selectivity. Computational and in vitro studies have proposed cellular mechanisms of gain modulation based on the postsynaptic effects of background synaptic activation, but these mechanisms have not been studied in vivo. Here, we used intracellular recordings from cat primary visual cortex to measure neuronal gain while changing background synaptic activity with visual stimulation.

Stimulus feature selectivity in excitatory and inhibitory neurons in primary visual cortex.

Although several lines of evidence suggest that stimulus selectivity in somatosensory and visual cortices is critically dependent on unselective inhibition, particularly in the thalamorecipient layer 4, no comprehensive comparison of the responses of excitatory and inhibitory cells has been conducted. Here, we recorded intracellularly from a large population of regular spiking (RS; presumed excitatory) and fast spiking (FS; presumed inhibitory) cells in layers 2-6 of primary visual cortex. In layer 4, where selectivity for orientation and spatial frequency first emerges, we found no untuned FS cells.

Precision, reliability, and information-theoretic analysis of visual thalamocortical neurons.

High-order statistics of neural responses allow one to gain insight into neural function that may not be evident from firing rate alone. In this study, we compared the precision, reliability, and information content of spike trains from X- and Y-cells in the lateral geniculate nucleus (LGN) and layer IV simple cells of area 17 in the cat. To a stochastic, contrast-modulated Gabor patch, layer IV simple cells responded as precisely as their primary inputs, LGN X-cells, but less reliably.

Stimulus-dependent gamma (30-50 Hz) oscillations in simple and complex fast rhythmic bursting cells in primary visual cortex.

Oscillatory activity is generated by many neural systems. gamma band (approximately 40 Hz) oscillations in the thalamus and cortex occur spontaneously and in response to sensory stimuli. Fast rhythmic bursting (FRB) cells (also called chattering cells) comprise a unique class of cortical neurons that, during depolarization by current injection, intrinsically generate bursts of high-frequency action potentials with an interburst frequency between 30 and 50 Hz.

Visual detection deficits following inactivation of the superior colliculus in the cat.

Lesion or inactivation of the superior colliculus (SC) of the cat results in an animal that fails to orient toward peripheral visual stimuli which normally evoke a brisk, reflexive orienting response. A failure to orient toward a visual stimulus could be the result of a sensory impairment (a failure to detect the visual stimulus) or a motor impairment (an inability to generate the orienting response). Either mechanism could explain the deficit observed during SC inactivation since neurons in the SC can carry visual sensory signals as well as motor commands involved in the generation of head and eye movements.

Effects of surround motion on receptive-field gain and structure in area 17 of the cat.

Modulation of responses elicited by moving bars within the classical receptive fields (CRF) of cat area 17 neurons were studied as a function of the direction and velocity of drifting gratings in the surrounds. Several different types of modulation were observed; collectively, the responses of most cells, both simple and complex, were strongly modulated by surround motion. None of these cells appear to signal relative velocity between the CRF and its surround.