Receptive field properties of visual cortical neurons depend on the spatiotemporal context within which the stimuli are presented. We have examined the temporal context dependence of cortical orientation tuning using dynamic visual stimuli with rapidly changing orientations. We found that tuning to the orientation of the test stimulus depended on a briefly presented preceding stimulus, with the preferred orientation shifting away from the preceding orientation. Analyses of the spatial-phase dependence of the shift showed that the effect cannot be explained by purely feedforward mechanisms, but can be accounted for by activity-dependent changes in the recurrent interactions between different orientation columns. Thus, short-term plasticity of the intracortical circuit can mediate dynamic modification of orientation tuning, which may be important for efficient visual coding.

Motion signals in the visual field can cause strong biases in the perceived positions of stationary objects. Local motion signal within an object induces a shift in the perceived object position in the direction of motion, whereas adaptation to motion stimuli causes a perceptual shift in the opposite direction. The neural mechanisms underlying these illusions are poorly understood. Here we report two novel receptive field (RF) properties in cat primary visual cortex that may account for these motion-position illusions. First, motion signal in a stationary test stimulus causes a displacement of the RF in the direction opposite to motion. Second, motion adaptation induces a shift of the RF in the direction of adaptation. Comparison with human psychophysical measurements under similar conditions indicates that these RF properties can primarily account for the motion-position illusions. Importantly, both RF properties indicate a spatial asymmetry in the synaptic connections from direction-selective cells, and this circuit feature can be predicted by spike-timing-dependent synaptic plasticity, a widespread phenomenon in the nervous system. Thus, motion-induced perceptual mislocalization may be mediated by asymmetric cortical circuits, as a natural consequence of experience-dependent synaptic modification during circuit development.

In the motion-extrapolation hypothesis, the visual system can extrapolate the instantaneous position of a moving object from its past trajectory. The existence of such a mechanism in human vision has been intensely debated. Here, we show compelling perceptual extrapolation of both first- and second-order moving stimuli, the magnitude of which depends on blurring of the visual target. The spatiotemporal characteristics of the extrapolation can be quantitatively accounted for by a simple model based on temporally biphasic neuronal response, a property widely observed among sensory neurons. Thus, motion-induced perceptual extrapolation exists in human vision, and spatial blurring is an important factor in the interaction between motion and perceptual localization.

Visual stimuli are known to induce various changes in the receptive field properties of adult cortical neurons, but the underlying mechanisms are not well understood. Repetitive pairing of stimuli at two orientations can induce a shift in cortical orientation tuning, with the direction and magnitude of the shift depending on the temporal order and interval between the pair. Although the temporal specificity of the effect on the order of tens of milliseconds strongly suggests spike-timing-dependent synaptic plasticity (STDP) as the underlying mechanism, it remains unclear whether the modification occurs within the cortex or at earlier stages of the visual pathway. In the present study, we examined the involvement of an intracortical mechanism in this functional modification. First, we measured interocular transfer of the shift induced by monocular conditioning. We found complete transfer of the effect at both the physiological and psychophysical levels, indicating that the modification occurs largely in the cortex. Second, we analyzed the spike timing of cortical neurons during conditioning and found it commensurate with the requirement of STDP. Finally, we compared the measured shift in orientation tuning with the prediction of a model circuit that exhibits STDP at intracortical connections. This model can account for not only the temporal specificity of the effect but also the dependence of the shift on both orientations in the conditioning pair. These results indicate that modification of intracortical connections is a key mechanism in the stimulustiming-dependent plasticity in orientation tuning.V isual stimuli are known to induce various changes in adult cortical circuits. For example, in contrast adaptation, a few seconds of visual stimulation can cause a marked reduction in the response amplitude of cortical neurons (1) along with changes in their spatial frequency tuning (2), orientation tuning (3, 4), and direction selectivity (5). These effects may be caused by a reduction in neuronal excitability (6, 7) or by short-term synaptic depression (8). Concurrent visual stimulation and iontophoretic activation of cortical neurons can induce changes in their orientation selectivity and ocular dominance (9-11). The dependence of these effects on the coincidence between visual and iontophoretic stimulation is consistent with Hebb's rule for synaptic modification. Similarly, synchronous stimulation of the receptive field (RF) center and part of the surround can induce an RF expansion toward the costimulated surround (12), which is also likely mediated by Hebbian synaptic modification. Together, these studies indicate a high degree of plasticity of adult cortical circuits. In this study, we focused on a form of cortical modification that is likely mediated by spike-timing-dependent synaptic plasticity (STDP) of synaptic connections.In STDP, the direction and magnitude of synaptic modification depend on the order and interval between the pre-and postsynaptic spikes: Presynaptic spiking within tens of milliseconds be...

Recent studies show that synaptic modification depends critically on the relative spike timing of pre- and postsynaptic neurons. Here we explore the functional implications of spike timing-dependent synaptic plasticity in the visual cortex using a model circuit with modifiable intracortical excitatory connections. First we simulated the experiments using two-point stimuli, in which two visual stimuli in a topographically represented feature space were repeatedly presented in quick succession, and found that tuning of the cortical neurons was modified in a manner similar to that observed experimentally. We then explored the dependence of results on the model parameter and identified the intracortical parameters that were critical for the magnitude of the shifts and obtained a simple relationship between the amount of shift and (S=(sigmaEXTCrec_exc)/sigmaINHCrec_inh). Finally we investigated the effects of moving stimuli in a topographically represented visual space and found that they can effectively induce spike timing-dependent modification of the intracortical connections. It suggests the importance of moving stimuli in dynamic modification of the cortical maps through spike timing-dependent synaptic plasticity.