Biology subjects

Morales-Torres, R.

Publications and source records attributed to Morales-Torres, R..

3 recordsLinked to original sources

bioRxiv2025

Exploring Auditory Category Distinctions in Perception and Imagery

Imagery, the ability to generate perceptual experiences in the absence of external stimuli, is used every day when remembering a past event or imagining a novel situation. While most previous research on imagery has focused on the visual domain, the present study presents an investigation of auditory imagery. The perception of different categories of sound has been shown to evoke different neural responses. Further, the neural processes underlying auditory imagery and perception have been shown to be similar. Therefore, we hypothesized that auditory imagery would rely on similar categorical processing. Participants learned shape-sound associations and were then asked to imagine the matching sound when presented with the associated shape. We chose two example stimuli from two maximally different sound categories -- human speech sounds and nonhuman environmental sounds -- to investigate our hypothesis. Electroencephalography (EEG) data were recorded while participants listened to and imagined the sounds. The mean voltage in the P2 event-related potential time window (180-280 ms) was significantly larger for perception of the speech sounds than the environmental sounds, and the late positive event-related potential complex (LPC, 350-500 ms) associated with imagery was significantly smaller for imagery of the speech sounds than the environmental sounds. This suggests that, as in perception, the neural processing of imagined sounds is categorical.

neuroscience↗

bioRxiv2025

Trial-Level Representational Similarity Analysis

Neural representation refers to the brain activity that stands in for ones cognitive experience, and in cognitive neuroscience, a prominent method of studying neural representations is representational similarity analysis (RSA). While there are several recent advances in RSA, the classic RSA (cRSA) approach examines the structure of representations across numerous items by assessing the correspondence between two representational similarity matrices (RSMs): usually one based on a theoretical model of stimulus similarity and the other based on similarity in measured neural data. However, because cRSA cannot weigh the contributions of individual trials (RSM rows/columns), it is fundamentally limited in its ability to assess subject-, stimulus-, and trial-level variances that all influence representation. Here, we formally introduce trial-level RSA (tRSA), an analytical framework that estimates the strength of neural representation for singular experimental trials and evaluates hypotheses using multi-level models. First, we verified the correspondence between tRSA and cRSA in quantifying the overall representation strength across all trials. Second, we compared the statistical inferences drawn from both approaches using simulated data that reflected a wide range of scenarios. Compared to cRSA, the multi-level framework of tRSA was both more theoretically appropriate and significantly sensitive to true effects. Third, using real fMRI datasets, we further demonstrated several issues with cRSA, to which tRSA was more robust. Finally, we presented some novel findings of neural representations that could only be assessed with tRSA and not cRSA. In summary, tRSA proves to be a robust and versatile analytical approach for cognitive neuroscience and beyond.

neuroscience↗

bioRxiv2024

Using Dual-Coil TMS-EEG to Probe Bilateral Brain Mechanisms in Healthy Aging and Mild Cognitive Impairment

BackgroundA widespread observation in the cognitive neuroscience of aging is that older adults show a more bilateral pattern of task-related brain activation. These observations are based on inherently correlational approaches. The current study represents a targeted assessment of the role of bilaterality using repetitive transcranial magnetic stimulation (rTMS). ObjectiveWe used a novel bilateral TMS-stimulation paradigm, applied to a group of healthy older adults (hOA) and older adults with mild cognitive impairment (MCI), with two aims: First, to elucidate the neurophysiological effects of bilateral neuromodulation, and second to provide insight into the neurophysiological basis of bilateral brain interactions. MethodsElectroencephalography (EEG) was recorded while participants received six forms of transcranial magnetic stimulation (TMS): unilateral and bilateral rTMS trains at an alpha (8 Hz) and beta (18 Hz) frequency, as well as two sham conditions (unilateral, bilateral) mimicking the sounds of TMS. ResultsFirst, time-frequency analyses of oscillatory power induced by TMS revealed that unilateral beta rTMS elicited rhythmic entrainment of cortical oscillations at the same beta-band frequency. Second, both bilateral alpha and bilateral beta stimulation induced a widespread reduction of alpha power. Lastly, healthy older adults showed greater TMS-related reductions in alpha power in response to bilateral rTMS compared to the MCI cohort. ConclusionOverall, these results demonstrate frequency-specific responses to bilateral rTMS in the aging brain, and provide support for inhibitory models of hemispheric interaction across multiple frequency bands.

neuroscience↗