Sound power modulates rat visual perception and neuronal tuning in rat primary visual cortex

In the last decade, a range of structural and functional studies in rodents uncovered multisensory interactions within early sensory areas. For instance, noise bursts led to the hyperpolarization of V1 neurons in the absence of visual stimulation, with the extent of this inhibition correlating with noise power. Additionally, V1 neurons were found to be sensitive to the temporal coherence between auditory and visual stimuli. Nevertheless, the influence of these interactions on perception and decision-making remained elusive. To investigate this, we trained ten rats in a visual temporal frequency classification task, assessing the potential impact of task-irrelevant, temporally congruent or incongruent sounds on their perception. Our findings revealed that while auditory stimuli modulated visual perception, their temporal coherence did not enhance rat performance compared to incongruent pairs. Intriguingly, rat performance showed a notable correlation with the intensity of the auditory stimuli, suggesting that the encoding of temporal frequency in V1 may be shaped by the power of sound, rather than audiovisual temporal coherence. We hypothesized that: i) sound inhibits the encoding of the temporal frequency of visual stimuli in V1 according to its power; ii) the firing rate of V1 neurons is proportional to the temporal frequency of the visual stimuli. We incorporated these assumptions into an Ideal Observer model, which significantly predicted the observed responses in the task. In addition, we aimed to investigate these effects at the neuronal level by performing extracellular recordings in V1 of anesthetized rats. Preliminary analyses of neuronal tuning curves to visual temporal frequency uncovered a trend of monotonically increasing firing rate in line with the stimuli' temporal frequencies, affirming our assumptions. Lastly, we observed substantial differences in neuronal tuning when temporally modulated visual stimuli were combined with sounds of varying power. Specifically, responses decreased for sounds with higher amplitude power. Collectively, these findings reinforce the idea that multisensory processing takes place within the sensory cortices of rodents and unveil preliminary evidence of these processes influencing perception and decision-making.