4/5/2023 0 Comments Gamma control v4![]() Succeeding studies ( Treue and Maunsell, 1996 Luck et al., 1997 Chelazzi et al., 1998 Reynolds et al., 1999) confirmed for various visual areas that the neuronal firing rates can reflect even less preferred stimuli while optimal stimuli are present at the same time. In contrast, when allocating attention to one of the two simultaneously presented stimuli, the neuron's firing rate resembled its response when the stimulus was presented alone. They found for neurons in visual areas V4 and IT that placing a preferred and a nonpreferred stimulus together in the RF resulted in an intermediate firing rate response of the neurons compared with the responses when the stimuli were presented alone. In a now classical experiment aiming to demonstrate such selective processing on the neuronal level, Moran and Desimone (1985) placed either one, or two stimuli in a neuron's receptive field (RF). Selective attention is required to focus on parts of the continuous stream of incoming information about the environment, thereby allowing for advanced processing like shape perception of individual stimuli embedded in cluttered visual scenes ( Rock and Gutman, 1981 Rock et al., 1992 Wolfe and Bennett, 1997). The method provides a useful tool to study mechanisms of dynamic network configuration underlying cognitive processes. Importantly, the attended signals did not need to be amplified already in an earlier processing stage, nor did they get amplified by a simple output response modulation. A minimal model demonstrated that coherent gamma-rhythmic activity (∼60 Hz) between local neurons and their afferent-providing input neurons can realize the gating. We found that attention “gates” signals at the interplay between afferent fibers and the local neurons. We designed an experiment that allows to causally assess routing of information originating from an attended object. SIGNIFICANCE STATEMENT Depending on the behavioral context, the brain needs to channel the flow of information through its networks of massively interconnected neurons. It supports the proposal that selective interareal gamma-band synchrony subserves signal routing and explains our experimental finding that attention selectively gates signals already at the level of afferent synaptic input. A minimal model implementing attention-dependent routing by gamma-band synchrony replicated the attentional gating effect and the signals' spectral transfer characteristics. Our results rather imply that selective attention uses a gating mechanism comprising the synaptic “inputs” that transmit signals from upstream areas into the V4 neurons. Furthermore, our results show that attention does not need to modulate responses in the input populations sending signals to V4 to selectively represent a stimulus, nor do they suggest a change of the V4 neurons' output gain depending on their feature similarity with the stimuli. This new experimental paradigm revealed that signal transmission was considerably weaker for the not-attended stimulus. To investigate this question, we tagged two equivalent visual stimuli by independent broadband luminance noise and used the spectral coherence of these behaviorally irrelevant signals with the field potential of a local neuronal population in male macaque monkeys' area V4 as a measure for their respective causal influences. Unclear is where in the neuronal pathway attention intervenes to achieve such selective signal routing and processing. Their spiking response then resembles the response to the attended stimulus when presented in isolation. Neurons in the extrastriate visual cortex reflect such selective processing when different stimuli are simultaneously present in their large receptive fields. Selective attention allows focusing on only part of the incoming sensory information.
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