Separable gain control of ongoing and evoked activity in the visual cortex by serotonergic input

Controlling gain of cortical activity is essential to modulate weights between internal ongoing communication and external sensory drive. Here, we show that serotonergic input has separable suppressive effects on the gain of ongoing and evoked visual activity. We combined optogenetic stimulation of the dorsal raphe nucleus (DRN) with wide-field calcium imaging, extracellular recordings, and iontophoresis of serotonin (5-HT) receptor antagonists in the mouse visual cortex. 5-HT1A receptors promote divisive suppression of spontaneous activity, while 5-HT2A receptors act divisively on visual response gain and largely account for normalization of population responses over a range of visual contrasts in awake and anesthetized states. Thus, 5-HT input provides balanced but distinct suppressive effects on ongoing and evoked activity components across neuronal populations. Imbalanced 5-HT1A/2A activation, either through receptor-specific drug intake, genetically predisposed irregular 5-HT receptor density, or change in sensory bombardment may enhance internal broadcasts and reduce sensory drive and vice versa.

Processing bias: extending sensory drive to include efficacy and efficiency in information processing

Communication signals often comprise an array of colours, lines, spots, notes or odours that are arranged in complex patterns, melodies or blends. Receiver perception is assumed to influence preference and thus the evolution of signal design, but evolutionary biologists still struggle to understand how perception, preference and signal design are mechanistically linked. In parallel, the field of empirical aesthetics aims to understand why people like some designs more than others. The model of processing bias discussed here is rooted in empirical aesthetics, which posits that preferences are influenced by the emotional system as it monitors the dynamics of information processing and that attractive signals have effective designs that maximize information transmission, efficient designs that allow information processing at low metabolic cost, or both. We refer to the causal link between preference and the emotionally rewarding experience of effective and efficient information processing as the processing bias, and we apply it to the evolutionary model of sensory drive. A sensory drive model that incorporates processing bias hypothesizes a causal chain of relationships between the environment, perception, pleasure, preference and ultimately the evolution of signal design, both simple and complex.

Songs in the understory and colors in the canopy: habitat structure leads to different avian communication strategies in a tropical montane forest

Birds inhabit a variety of habitats and they communicate using primarily visual and acoustic signals; two central hypotheses have been postulated to study the evolution of such a signals. The sensory drive hypothesis posits that variation in the physical properties of habitats leads to variation in natural selection pressures by affecting the ease with which different types of signals are perceived. Assuming that resources are limited for animals, the transfer hypothesis predicts a negative relationship between the investments in different types of signals. We evaluated these two hypotheses in a tropical montane forest bird assemblage. We also postulate a possible interaction between these two hypotheses: we predicted that the negative relationships between signals should be observed only when jointly considering birds from different environments (e.g. understory and canopy) due to the expected differences in communication strategies between habitats. The sensory drive hypothesis was supported by the differences we found between strata in vocal output, patch contrast to background and color conspicuousness, but not for the variables associated to song elaboration and hue disparity. We found support for the transfer hypothesis: birds with colors contrasting less against the background sing more frequently and birds with lower diversity of colors produce longer songs, understory birds showed also a negative relationship between signals, but only when accounting for phylogeny. We found partial support for the interaction between the sensory drive and the transfer hypotheses: hue disparity and vocal output were negatively related only when analyzing together birds from the canopy and the understory, but not when analyzing them separately. We conclude that the study of the evolution of communication signals needs to consider more than one channel and the functional interactions between them. The results of the interaction of optimal signaling strategies in two communication channels in the local habitats where animals signaling, are the patterns of colors and songs we revealed in a tropical montane forest bird assemblage.