Biology subjects

Schmehl, M. N.

Publications and source records attributed to Schmehl, M. N..

3 recordsLinked to original sources

bioRxiv2025

Multiplexing of visual-auditory signals in a predominantly auditory brain region

A recently proposed theory of neural representation postulates that when more than one stimulus is to be encoded, neurons in that representation may fluctuate between encoding each item. To date, such work has considered only cases in which both stimuli are of the same sensory modality, such as how two sounds are encoded in an auditory brain region. Here, we consider the influence of sensory modality on this process, asking whether stimuli of a non-dominant sensory modality can evoke or influence the fluctuating activity patterns observed for combinations of stimuli of a dominant sensory modality. Specifically, we investigated the impact of combining visual and auditory stimuli on single-unit activity in the inferior colliculus, a predominantly auditory structure, in monkeys performing a behavioral task involving reporting all stimulus locations in a given trial. We found that fluctuating activity is evident when a single sound and a single visual stimulus are paired at the same spatial location, indicating that fluctuating activity can be induced when one item is not from a brain areas preferred modality, and even when only a single spatial location is involved and spatial attention is directed to only one place. Fluctuating activity was also identified when visual stimuli were paired with sounds presented at two spatial locations. The IC appeared to maintain a representation of all stimuli, regardless of the sequence in which the monkey localized the targets (although in one monkey there was a bias toward greater representation of the second reported location). Together, these results indicate that fluctuating activity occurs in response to multimodal stimuli in a predominantly unimodal brain structure and is geared toward preservation of all sensory information rather than attentional filtering. Impact StatementWe found that when visual stimuli are paired with sounds, they can induce fluctuating activity in neurons that are primarily sensitive to sound alone. Such activity fluctuations may permit the representation of both the visual and auditory stimuli in an overlapping population of neurons.

neuroscience↗

bioRxiv2024

Visually-evoked activity and variable modulation of auditory responses in the macaque inferior colliculus

How multisensory cues affect processing in early sensory brain areas is not well understood. The inferior colliculus (IC) is an early auditory structure that is visually responsive (Porter et al. 2007; Bulkin and Groh 2012a, 2012b), but little is known about how visual signals affect the ICs auditory representation. We explored how visual cues affect both spiking and local field potential (LFP) activity in the IC of two monkeys performing a task involving saccades to auditory, visual, or combined audiovisual stimuli. We confirm that LFPs are sensitive to the onset of fixation lights as well as the onset of visual targets presented during steady fixation. The LFP waveforms evoked by combined audiovisual stimuli differed from those evoked by sounds alone. In single-unit spiking activity, responses were weak when visual stimuli were presented alone, but visual stimuli could modulate the activity evoked by sounds in a stronger way. Such modulations could involve either increases or decreases in activity, and whether increases or decreases were observed was variable and not obviously correlated with the responses evoked by visual or auditory stimuli alone. These findings indicate that visual stimuli shape the ICs auditory representation in flexible ways that differ from those observed previously in multisensory areas. New & NoteworthyWe find that the inferior colliculus, a primarily auditory brain area, displays distinct population-level responses to visual stimuli. We also find that visual cues can influence the auditory responses of individual neurons. Together, the results provide insight into how relatively early sensory areas may play a role in combining multiple sensory modalities to refine the perception of complex environments.

neuroscience↗

bioRxiv2023

Multiple objects evoke fluctuating responses in several regions of the visual pathway

How neural representations preserve information about multiple stimuli is mysterious. Because tuning of individual neurons is coarse (for example, visual receptive field diameters can exceed perceptual resolution), the populations of neurons potentially responsive to each individual stimulus can overlap, raising the question of how information about each item might be segregated and preserved in the population. We recently reported evidence for a potential solution to this problem: when two stimuli were present, some neurons in the macaque visual cortical areas V1 and V4 exhibited fluctuating firing patterns, as if they responded to only one individual stimulus at a time (Jun et al., 2022). However, whether such an information encoding strategy is ubiquitous in the visual pathway and thus could constitute a general phenomenon remains unknown. Here we provide new evidence that such fluctuating activity is also evoked by multiple stimuli in visual areas responsible for processing visual motion (middle temporal visual area, MT), and faces (middle fundus and anterolateral face patches in inferotemporal cortex - areas MF and AL), thus extending the scope of circumstances in which fluctuating activity is observed. Furthermore, consistent with our previous results in the early visual area V1, MT exhibits fluctuations between the representations of two stimuli when these form distinguishable objects but not when they fuse into one perceived object, suggesting that fluctuating activity patterns may underlie visual object formation. Taken together, these findings point toward an updated model of how the brain preserves sensory information about multiple stimuli for subsequent processing and behavioral action. Impact StatementNeural fluctuations in multiple areas along the visual cortical hierarchy could allow the brain to represent distinct co-occurring visual stimuli.

neuroscience↗