Contextual signals in visual cortex:How sounds, state, and task setting shape how we see

What we see is not always what we get. Even though the light that hits the retina might convey the same images, how visual information is processed and what we eventually do with it depend on many contextual factors. In this thesis, we show in a series of experiments how the sensory processing of the same visual input in the visual cortex of mice is affected by our internal state, movements, other senses and any task we are performing. We found that recurrent activity originating within higher visual areas modulates activity in the primary visual cortex (V1) and selectivity amplifies weak compared to strong sensory-evoked responses. Second, visual stimuli evoked similar early activity in V1, but later activity strongly depended on whether mice were trained to report the visual stimuli, and on the specific task. Specifically, adding a second modality to the task demands extended the temporal window during which V1 was causally involved in visual perception. Third, we report that not only visual stimuli but also sounds led to strong responses in V1, composed of distinct auditory-related and motor-related activity. Finally, we studied the role of Posterior Parietal Cortex in an audiovisual change detection task. Despite extensive single-neuron and population-level encoding of task-relevant visual and auditory stimuli, as well as upcoming behavioral responses, optogenetic inactivation did not affect task performance. Whereas these contextual factors have previously been studied in isolation, we obtain a more integrated understanding of how factors beyond visual information determine what we actually see

Multisensory task demands temporally extend the causal requirement for visual cortex in perception

Primary sensory areas constitute crucial nodes during perceptual decision making. However, it remains unclear to what extent they mainly constitute a feedforward processing step, or rather are continuously involved in a recurrent network together with higher-order areas. We found that the temporal window in which primary visual cortex is required for the detection of identical visual stimuli was extended when task demands were increased via an additional sensory modality that had to be monitored. Late-onset optogenetic inactivation preserved bottom-up, early-onset responses which faithfully encoded stimulus features, and was effective in impairing detection only if it preceded a late, report-related phase of the cortical response. Increasing task demands were marked by longer reaction times and the effect of late optogenetic inactivation scaled with reaction time. Thus, independently of visual stimulus complexity, multisensory task demands determine the temporal requirement for ongoing sensory-related activity in V1, which overlaps with report-related activity

Contextual signals in visual cortex: How sounds, state, and task setting shape how we see

What we see is not always what we get. Even though the light that hits the retina might convey the same images, how visual information is processed and what we eventually do with it depend on many contextual factors. In this thesis, we show in a series of experiments how the sensory processing of the same visual input in the visual cortex of mice is affected by our internal state, movements, other senses and any task we are performing. We found that recurrent activity originating within higher visual areas modulates activity in the primary visual cortex (V1) and selectivity amplifies weak compared to strong sensory-evoked responses. Second, visual stimuli evoked similar early activity in V1, but later activity strongly depended on whether mice were trained to report the visual stimuli, and on the specific task. Specifically, adding a second modality to the task demands extended the temporal window during which V1 was causally involved in visual perception. Third, we report that not only visual stimuli but also sounds led to strong responses in V1, composed of distinct auditory-related and motor-related activity. Finally, we studied the role of Posterior Parietal Cortex in an audiovisual change detection task. Despite extensive single-neuron and population-level encoding of task-relevant visual and auditory stimuli, as well as upcoming behavioral responses, optogenetic inactivation did not affect task performance. Whereas these contextual factors have previously been studied in isolation, we obtain a more integrated understanding of how factors beyond visual information determine what we actually see

Functional (ir)relevance of posterior parietal cortex during audiovisual change detection

The posterior parietal cortex (PPC) plays a key role in integrating sensory inputs from different modalities to support adaptive behavior. Neuronal activity in PPC reflects perceptual decision-making across behavioral tasks, but the mechanistic involvement of PPC is unclear. In an audiovisual change detection task, we tested the hypothesis that PPC is required to arbitrate between the noisy inputs from the two different modalities and help decide in which modality a sensory change occurred. In trained male mice, we found extensive single-neuron and population-level encoding of task-relevant visual and auditory stimuli, trial history, as well as upcoming behavioral responses. However, despite these rich neural correlates, which would theoretically be sufficient to solve the task, optogenetic inactivation of PPC did not affect visual or auditory performance. Thus, despite neural correlates faithfully tracking sensory variables and predicting behavioral responses, PPC was not relevant for audiovisual change detection. This functional dissociation questions the role of sensory- and task-related activity in parietal associative circuits during audiovisual change detection. Furthermore, our results highlight the necessity to dissociate functional correlates from mechanistic involvement when exploring the neural basis of perception and behavior. SIGNIFICANCE STATEMENT The posterior parietal cortex (PPC) is active during many daily tasks, but capturing its function has remained challenging. Specifically, it is proposed to function as an integration hub for multisensory inputs. Here, we tested the hypothesis that, rather than classical cue integration, mouse PPC is involved in the segregation and discrimination of sensory modalities. Surprisingly, although neural activity tracked current and past sensory stimuli and reflected the ongoing decision-making process, optogenetic inactivation did not affect task performance. Thus, we show an apparent redundancy of sensory and task-related activity in mouse PPC. These results narrow down the function of parietal circuits, as well as direct the search for those neural dynamics that causally drive perceptual decision-making