Biology subjects

Mehmood, I.

Publications and source records attributed to Mehmood, I..

5 recordsLinked to original sources

bioRxiv2025

Temporal boundary gating of auditory sensitivity

Perception unfolds over time, but whether continuous sounds are sampled with uniform sensitivity is unknown. We combine human psychophysics, EEG and rodent neurophysiology to show that local auditory change detection is strongly gated by stimulus boundaries. In humans, brief perturbations inserted at different temporal positions within 0.5-1-s tones revealed an inverted U-shaped sensitivity profile: detection was attenuated near sound onset and offset and maximal mid-epoch, with EEG change responses showing a closely matching dependence on change timing. Electrocorticography in awake rats exhibited homologous temporal weighting, and analogous profiles for amplitude changes and visual motion demonstrated cross-feature and cross-modal generality. To uncover circuit mechanisms, we recorded single units along the inferior colliculus-medial geniculate body-auditory cortex pathway together with laminar local field potentials in A1. Onset-locked suppression of change responses emerged in midbrain and was progressively amplified in thalamus and cortex, whereas the full start-end profile was expressed in granular-layer alpha-gamma power. A simple biophysically grounded model in which onset responses saturate and cortical populations integrate over finite temporal windows recapitulates this pattern, explaining how stimulus boundaries disrupt prospective and retrospective integration and thereby degrade change detection near the beginning and end of sounds.

neuroscience↗

bioRxiv2025

Echoes as Signal, Not Noise: Reverberation Sharpens Sensitivity to Temporal Structure

Sensitivity to temporal structure is fundamental to hearing, yet how natural reverberation shapes this sensitivity is unclear. Here we identify echo-facilitated temporal sensitivity (EFTS), a principle whereby the auditory system exploits echoes to selectively enhance responses to rapid temporal changes. Using transitional click trains with subtle inter-click-interval (ICI) shifts, we first show that increasing echo strength systematically enlarges the sound-level step at ICI transitions in both recorded and simulated stimuli, sharpening the physical boundary between segments of distinct temporal structure. In humans, psychophysical detection of ICI changes improves monotonically with echo level in both simulated and real free-field environments, while a late EEG change response scales with echo strength as onset responses remain comparatively stable. In awake rats, electrocorticography over auditory cortex reveals parallel echo-dependent enhancement of transition-evoked activity. Single units exhibit echo-level-dependent amplification of change-related firing and improved neurometric discriminability. Laminar local field potential and current source density analyses further show that echo-dependent divergence emerges first in granular and infragranular layers before propagating to supragranular cortex, consistent with thalamocortical drive followed by intracortical amplification. Together, these findings establish EFTS as a cross-species mechanism that reframes echoes as structured signals the brain uses to sharpen temporal integration in everyday listening.

neuroscience↗

bioRxiv2025

Comparison and Dynamic interaction between Auditory Cortex and Prefrontal Cortex of Behaving Monkeys during Novelty Detection

The ability to detect deviations from expected sensory input is fundamental for adaptive behavior. We recorded electrocorticographic activity from the auditory (AC) and prefrontal (PFC) cortices of behaving macaques during an auditory oddball task to probe the cortical dynamics of predictive processing. Repetition of standard stimuli evoked suppression and facilitation in AC and strong low-frequency (2 Hz) enhancement in PFC, accompanied by bidirectional delta-band coupling indicative of a shared predictive state. Deviant stimuli triggered early AC responses followed by PFC activation and increased feedforward and feedback connectivity across delta, theta, and gamma bands. Behavioral engagement amplified both prediction and prediction error signals, strengthening cortical network coordination. Together, these findings reveal a hierarchical predictive network in which the AC encodes sensory regularities and violations, while the PFC integrates predictive context in a behaviorally dependent manner.

neuroscience↗

bioRxiv2024

Temporal Configuration as a New Feature of Sound: Psychological and Neurophysiological Evidence, Cross-species Consistency and Underlying Neuronal Mechanisms

Natural sounds are defined not only by their spectral content but also by their fine temporal structure. Here we show that millisecond-scale temporal configuration--defined by the ordering of inter-click intervals (ICIs) within a click train--behaves as a distinct auditory feature, conserved across species and emerging hierarchically along the auditory pathway. Human listeners reliably discriminated click trains that shared the same average ICI but differed in temporal configuration, and these differences elicited robust mismatch negativity (MMN) responses in an oddball paradigm, indicating automatic cortical deviance detection. Awake rats showed analogous MMN-like ECoG responses to configuration changes, demonstrating cross-species generality. Neuropixels recordings along the inferior colliculus-medial geniculate body-primary auditory cortex (IC-MGB-A1) axis revealed minimal configuration sensitivity in IC, intermediate sensitivity in MGB, and strong stimulus-specific adaptation to temporal configuration in A1. Reversible cooling of auditory cortex reduced configuration sensitivity in MGB, implicating corticothalamic feedback in shaping thalamic representations. Layer-resolved analyses further showed that supragranular A1 neurons carry stronger configuration-specific adaptation than infragranular neurons. These findings identify temporal configuration as a feature-like dimension of sound and delineate a hierarchical, feedback-dependent IC-MGB-A1 circuit architecture for encoding fine temporal structure in the mammalian brain.

neuroscience↗

bioRxiv2024

A signal of temporal integration in the human auditory brain: psychological insights, EEG evidence, and clinical application

Temporal integration, the process by which the auditory system combines sound information over a curtain period to form a coherent auditory object, is essential for coherent auditory perception, yet its neural mechanisms remain underexplored. We use a "transitional click train" paradigm, which concatenates two click trains with slightly differing inter-click intervals (ICIs), to investigate temporal integration in the human cortex. Using a 64-channel electroencephalogram (EEG), we recorded responses from 42 healthy participants exposed to regular and irregular transitional click trains and conducted change detection tasks. Regular transitional click trains elicited significant change responses in the human cortex, indicative of temporal integration, whereas irregular trains did not. These neural responses were modulated by ICI length, ICI contrast, and regularity. Behavioral data mirrored EEG findings, showing enhanced detection for regular conditions compared to irregular conditions and pure tones. Furthermore, variations in change responses were associated with decision-making processes. Temporal continuity was critical, as introducing gaps between click trains diminished both behavioral and neural responses. In clinical assessments, 22 coma patients exhibited diminished or absent change responses, effectively distinguishing them from healthy individuals. Our findings identify distinct neural markers of temporal integration and highlight the potential of transitional click trains for clinical diagnostics.

neuroscience↗