Plieva, A. M. | Search bioRxiv

bioRxiv2026

Top-down attention modulates auditory sustained responses but not the neural processing advantage for vowels

Temporal and spectral regularities characteristic of vowels are preferentially encoded by the auditory system, giving rise to a prolonged enhancement of a negative electromagnetic response in the auditory cortex - sustained negativity (SN). However, it remains unclear how sustained attention to the auditory stream interacts with this intrinsically enhanced processing. Here, we used MEG to examine SN and its differential response to vowel-like acoustic patterns versus spectrally complex noise, while modulating subjects attention to the auditory stimulation. Four stimulus types (600 ms duration; vowel-like sounds with and without pitch, periodic non-vowel sounds, and aperiodic noise) were presented to 30 adults during passive listening and an active gap-detection task. In 16% of randomly selected trials, a 50-ms silent gap was inserted into the stimuli, which served as a target. The number of non-target trials between successive targets ranged from 1 to 10, with the highest probability corresponding to an interval of six trials. Only non-target trials were analyzed. Analysis of reaction times and omission errors indicated that target expectancy increased with the number of trials since the previous target. Task-related attention enhanced an early orienting-related negativity ([~]50-150 ms) across all stimulus types, irrespective of target expectancy. It also accelerated the processing of periodicity in non-vocal sounds but did not affect the processing of vowels. In contrast, the later segment of the SN (150-600 ms) was strongly modulated by proximity to the previous target, decreasing immediately after target events and increasing as the likelihood of target occurrence rose. Despite these attentional and expectancy-related modulations, the enhanced neural processing of periodic vowels relative to noise remained stable. These findings indicate that sustained attention modulates both early and late SN responses and accelerates the extraction of periodicity in non-vocal sounds, yet does not alter the neural advantage conferred by vowel-related regularities.

neuroscience↗

bioRxiv2025

Enhanced Neural Plasticity of the Primary Visual Cortex in Visual Snow Syndrome: Evidence from MEG Gamma Oscillations

Visual Snow Syndrome (VSS) is a neurological disorder characterized by persistent visual disturbances and associated symptoms. Although the neural basis of VSS remains poorly understood, it may involve increased neuronal excitability and/or altered neuroplasticity in the visual cortex, which could, in turn, affect visual gamma oscillations. An altered excitation-inhibition (E-I) balance is hypothesized to alter the modulation of gamma power and frequency by stimulation intensity, while maladaptive neuroplasticity may impact time-dependent changes in gamma power during repeated stimulation. To investigate potential alterations in E-I balance and neuroplasticity in VSS, we magnetoencephalography to record visual gamma oscillations in 26 VSS patients and 27 healthy controls. Participants were exposed to repeatedly presented high-contrast annular gratings, which were either static or drifting at varying speeds to systematically manipulate stimulation intensity. We also measured heart rate variability (HRV) during rest and repetitive visual stimulation to explore the relationship between time-dependent gamma changes and parasympathetic activation, which is known to promote activity-dependent plasticity. Our results showed no significant group differences in gamma power or frequency, nor in their modulation by drift rate, suggesting that the excitation-inhibition (E-I) balance in the primary visual cortex remains largely intact in VSS. Both groups exhibited an initial brief decrease in gamma power followed by a sustained linear increase with stimulus repetition, likely reflecting activity-dependent plasticity. HRV parameters were comparable across groups, with the parasympathetic-sympathetic balance index correlating with repetition-related increase in gamma power, further supporting the link between time-dependent gamma changes and neuroplasticity. Notably, VSS patients exhibited a steeper repetition-related increase in gamma power, indicating atypically heightened activity-dependent plasticity in this group. These findings provide the first experimental evidence suggesting that altered activity-dependent neuroplasticity plays a role in the pathophysiology of VSS. Furthermore, they identify repetition-related increases in gamma power as a potential biomarker of aberrant neuroplasticity, offering novel insights into VSS pathophysiology and potential avenues for targeted therapeutic interventions.

neuroscience↗