Biology subjects

Rajendran, V. G.

Publications and source records attributed to Rajendran, V. G..

6 recordsLinked to original sources

bioRxiv2024

Monkeys have rhythnm

Synchronizing movements to music is one of the hallmarks of human culture whose evolutionary and neurobiological origins remain unknown. The ability to synchronize movements requires 1) detecting a steady rhythmic pulse, or beat, out of a stream of complex sounds, 2) projecting this rhythmic pattern forward in time to predict future input, and 3) timing motor commands in anticipation of predicted future beats. Here, we demonstrate that the macaque is capable of synchronizing taps to a subjective beat in real music, and even spontaneously chooses to do so over alternative strategies. This contradicts the influential "vocal learning hypothesis" that musical beat synchronization is only possible in species with complex vocalizations such as humans and some songbirds. We propose an alternative view of musical beat perception and synchronization ability as a continuum onto which a wider range of species can be mapped depending on their ability to perform and coordinate the general abilities listed above through association with reward.

neuroscience↗

bioRxiv2023

Rats synchronize predictively to metronomes

Humans easily and naturally synchronize their motor activity to music, a behavior unparalleled by other species. As a consequence of the mystery surrounding its evolutionary and biological origins, there is rapidly growing interest in exploring the capacity of nonhuman species to synchronize motor activity with auditory rhythms. The hallmark observation in human studies is that synchronization is predictive. Given the highly variable behaviors observed in other animals, it is particularly difficult to distinguish a predictive synchronization behavior from one that perhaps resembles it, but relies on simpler strategies. Here, we introduce a novel modeling approach that quantitatively compares candidate strategies for explaining observed behaviors. Eight rats synchronized to metronomes across a range of tempi (0.5-2 Hz), and immediate water reward was delivered whenever they initiated a lick burst within a short time window around beats. We observed a roughly constant baseline lick probability throughout, with a [~]30% modulation of the lick rate around beats. We fitted to the results six candidate models, ranging from an insensitive model assuming that rats lick at random, to predictive models where rats suppress licking between beats for a tempo-dependent duration of time. The predictive model consistently outperformed other models, including a reactive model, demonstrating that rats synchronize predictively to auditory metronomes.

neuroscience↗

bioRxiv2022

Omission responses in field potentials but not spikes in rat auditory cortex

Non-invasive recordings of gross neural activity in humans often show responses to omitted stimuli in steady trains of identical stimuli. This has been taken as evidence for the neural coding of prediction or prediction error. However, evidence for such omission responses from invasive recordings of cellular-scale responses in animal models is scarce. Here, we sought to characterise omission responses using extracellular recordings in the auditory cortex of anaesthetised rats. We profiled omission responses across local field potentials (LFP), analogue multiunit activity (AMUA), and single/multi-unit spiking activity, using stimuli that were fixed-rate trains of acoustic noise bursts where 5% of bursts were randomly omitted. Significant omission responses were observed in LFP and AMUA signals, but not in spiking activity. These omission responses had a lower amplitude and longer latency than burst-evoked sensory responses, and omission response amplitude increased as a function of the number of preceding bursts. Contrary to theories of neural entrainment, rhythmic stimulus presentation did not increase low-frequency phase-locking of neural activity specific to the stimulus presentation rate. Together, our findings show that omission responses are observed in LFP and AMUA signals, with laminar specificity, but are not observed in spiking activity, and do not show evidence for low-frequency phase locking. This has implications for models of cortical processing that require many neurons to encode prediction error in their spike output, and may have some consistency with representation of error in dendrites electrotonically distant from the soma.

neuroscience↗

bioRxiv2021

Interaural Time Difference Tuning in the Rat Inferior Colliculus is Predictive of Behavioral Sensitivity

Recent studies have shown that rats are a useful model for binaural cochlear implant (CI) research, with behavioral sensitivity to interaural time differences (ITDs) of CI stimuli which are better than those of human patients. Here, we characterize ITD tuning in the rat inferior colliculus (IC) and explore whether quality of tuning can predict behavioral performance. We recorded IC responses to stimuli of varying pulse rates and envelope types and quantified both mutual information (MI) and neural d' as measures of ITD sensitivity. Neural d' values paralleled behavioral ones, declining with increasing click rates or when envelopes changed from rectangular to Hanning windows. While MI values increased with experience, neural d' did not. However, neural d' values correlated much better with behavioral performance than MI. Thus, neural d' appears to be a particularly well suited to predicting how stimulus parameters will impact behavioral performance.

neuroscience↗

bioRxiv2020

Memory Transfer of Random Time Patterns Across Modalities

Perception is sensitive to statistical regularities in the environment, including temporal characteristics of sensory inputs. Interestingly, temporal patterns implicitly learned within one modality can also be recognised in another modality. However, it is unclear how cross-modal learning transfer affects neural responses to sensory stimuli. Here, we recorded neural activity of human volunteers (N=24, 12 females, 12 males) using electroencephalography (EEG), while participants were exposed to brief sequences of randomly-timed auditory or visual pulses. Some trials consisted of a repetition of the temporal pattern within the sequence, and subjects were tasked with detecting these trials. Unknown to the participants, some trials reappeared throughout the experiment, enabling implicit learning. Replicating previous behavioural findings, we showed that participants benefit from temporal information learned in audition, and that they can apply this information to stimuli presented in vision. Such memory transfer was not observed from vision to audition. However, using an analysis of EEG response learning curves, we showed that learning temporal structures both within and across modalities modulates single-trial EEG response amplitudes in both conditions (audition to vision and vision to audition). Interestingly, the neural correlates of temporal learning within modalities relied on modality-specific brain regions, while learning transfer affected activity in frontal regions, suggesting distinct mechanisms. The cross-modal effect could be linked to frontal beta-band activity. The neural effects of learning transfer were similar both when temporal information learned in audition was transferred to visual stimuli and vice versa. Thus, both modality-specific mechanisms for learning of temporal information, and general mechanisms which mediate learning transfer across modalities, have distinct physiological signatures that are observable in the EEG.

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bioRxiv2018

Beat-Relevant Signals in Auditory Cortical Responses to Musical Excerpts

Musical beat perception is widely regarded as a high-level ability involving widespread coordination across brain areas, but how low-level auditory processing must necessarily shape these dynamics, and therefore perception, remains unexplored. Previous cross-species work suggested that beat perception in simple rhythmic noise bursts is shaped by neural transients in the ascending sensory pathway. Here, we found that low-level processes even substantially explain the emergence of beat in real music. Firing rates in the rat auditory cortex in response to twenty musical excerpts were on average higher on the beat than off the beat tapped by human listeners. This \"neural emphasis\" distinguished the perceived beat from alternative interpretations, was predictive of the degree of consensus across listeners, and was accounted for by a spectrotemporal receptive field model. These findings indicate that low-level auditory processing may have a stronger influence on the location and clarity of the beat in music than previously thought.

neuroscience↗