Adaptation in multisensory neurons: Impact on cross-modal enhancement

Abstract

Adaptation is a ubiquitous property of sensory neurons. Multisensory neurons, receiving convergent input from different sensory modalities, also likely exhibit adaptation. The responses of multisensory superior colliculus neurons have been extensively studied, but the impact of adaptation on these responses has not been examined. Multisensory neurons in the superior colliculus exhibit cross-modal enhancement, an often non-linear and non-additive increase in response when a stimulus in one modality is paired with a stimulus in a different modality. We examine the possible impact of adaptation on cross-modal enhancement within the framework of a simple model of adaptation for a neuron employing a saturating, logistic response function. We consider how adaptation to an input's mean and standard deviation affects cross-modal enhancement, and also how the statistical correlations between two different modalities influence cross-modal enhancement. We determine the optimal bimodal stimuli to present a bimodal neuron that evoke the largest changes in cross-modal enhancement under adaptation to input statistics. The model requires separate gains for each modality, unless the statistics specific to each modality have been standardised by prior adaptation in earlier, unisensory neurons. The model also predicts that increasing the correlation coefficient between two modalities reduces a multisensory neuron's overall gain.

Neural adaptation accounts for the dynamic resizing of peripersonal space: evidence from a psychophysical-computational approach

“…On the contrary, we assumed a negligible adaptation mechanism in the multisensory area (parameter G for the multisensory neurons, say G m , was set at a much smaller value than for unisensory neurons; see Table 1 for its default value, but also results for a sensitivity analysis on this parameter). This choice is justified to not violate the principle of multisensory integration according to which two bimodal stimuli presented sequentially (within 100–250 ms) produce enhancement and not depression of the multisensory neuron’s response ( Meredith et al 1987 ; Stein and Meredith 1993 ) and is in accord with studies suggesting that neural adaptation precedes ( Bruno et al 2010 ; Heron et al 2013 ) and benefits ( Elliott et al 2009 ) multisensory integration.…”

“…Second, the proposed model is equally able to account for the remapping of PPS as a function of sound velocity, ascribing this dynamic change to a neural adaptation to sustained stimulation. Importantly, the neural adaptation does not occur in the multisensory area (we assumed a negligible adaptation mechanism for the multisensory neurons), but in the upstream unisensory areas, as suggested in literature ( Bruno et al 2010 ; Elliott et al 2009 ; Heron et al 2013 ). Specifically, our network indicates that the sensitivity of the multisensory neuron to sound velocity is acquired through a coding mechanism of the sound velocity by the upstream auditory area, where adaptation takes place.…”

“…Indeed, neural adaptation is a pervasive phenomenon across the different sensory systems ( Barlow and Mollon 1982 ) and, interestingly, has been documented to closely reflect the natural statistics of the world ( Webster and Mollon 1997 ) in a similar fashion to multisensory processes ( Parise et al 2014 ; Stein and Meredith 1993 ). In fact, Elliott et al (2009) proposed that neural adaptation at unisensory areas shapes the neural input to multisensory areas in such a manner to optimize the emergence of multisensory enhancement.…”