Developmental Dyslexia (DD) is a neurobiological condition affecting the ability to read fluently and/or accurately. Analyzing resting-state electroencephalographic (EEG) activity in DD may provide a deeper characterization of the underlying pathophysiology and possible biomarkers. So far, studies investigating resting-state activity in DD provided limited evidence and did not consider the aperiodic component of the power spectrum. In the present study, adults with (n = 26) and without DD (n = 31) underwent a reading skills assessment and resting-state EEG to investigate potential alterations in aperiodic activity, their impact on the periodic counterpart and reading performance. In parieto-occipital channels, DD participants showed a significantly different aperiodic activity as indexed by a flatter and lower power spectrum. These aperiodic measures were significantly related to text reading time, suggesting a link with individual differences in reading difficulties. In the beta band, the DD group showed significantly decreased aperiodic-adjusted power compared to typical readers, which was significantly correlated to word reading accuracy. Overall, here we provide evidence showing alterations of the endogenous aperiodic activity in DD participants consistently with the increased neural noise hypothesis. In addition, we confirm alterations of endogenous beta rhythms, which are discussed in terms of their potential link with magnocellular-dorsal stream deficit.

Visual crowding is the difficulty in identifying an object when surrounded by neighbouring flankers, representing a bottleneck for object perception. Crowding arises not only from the activity of visual areas but also from parietal areas and fronto-parietal network activity. Parietal areas would provide the dorsal-to-ventral guidance for object identification and the fronto-parietal network would modulate the attentional resolution. Several studies highlighted the relevance of beta oscillations (15-25 Hz) in these areas for visual crowding and other connatural visual phenomena. In the present study, we investigated the differential contribution of beta oscillations in the parietal cortex and fronto-parietal network in the resolution of visual crowding. During a crowding task with letter stimuli, high-definition transcranial Alternating Current Stimulation (tACS) in the beta band (18 Hz) was delivered bilaterally on parietal sites, on the right fronto-parietal network, and in a sham regime. Resting-state EEG was recorded before and after stimulation to measure tACS-induced aftereffects. The influence of crowding was reduced only when tACS was delivered bilaterally on parietal sites. In this condition, beta power was reduced after the stimulation. Furthermore, the magnitude of tACS-induced aftereffects varied as a function of individual differences in beta oscillations. Results corroborate the link between parietal beta oscillations and visual crowding, providing fundamental insights on brain rhythms underlying the dorsal-to-ventral guidance in visual perception and suggesting that beta tACS can induce plastic changes in these areas. Remarkably, these findings open new possibilities for neuromodulatory interventions for disorders characterised by abnormal crowding, such as dyslexia.

Alpha oscillations (7-13 Hz) have been historically considered to shape temporal sampling processes in the visual modality, with faster alpha frequencies linked to finer temporal resolution. However, evidence is mostly correlational, and findings are not always replicated. Here, we investigated the role of alpha oscillations in temporal sampling using transcranial alternating current stimulation (tACS) and electroencephalography (EEG). Over three consecutive blocks, bilateral high-definition tACS was applied over extra-striate visual areas including V5/MT at either the individual alpha frequency (IAF), IAF+2, or IAF-2 Hz while participants performed a two flash fusion task. In line with previous findings, baseline resting-state IAF correlated with temporal segregation accuracy, with higher IAF predicting better segregation ability. Importantly, stimulation at IAF+2 Hz improved temporal segregation accuracy, whereas IAF-2 Hz decreased performance. This effect was specific for stimuli in the right hemifield, highlighting important hemispheric differences in alpha-mediated visual temporal sampling. Following stimulation, EEG data revealed no shift in the IAF and a decrease of alpha power independently from stimulation condition. Nonetheless, specifically for the IAF+2 stimulation, we observed a modulation of the aperiodic exponent of the power spectrum, indicating possible changes in cortical excitability as a short-term plasticity mechanism that persists beyond online tACS effects. Taken together, these results corroborate the role of alpha oscillations in defining temporal sampling processes and add novel evidence on the neurophysiological effects of tACS.

The present study investigated whether listeners can form abstract voice representations while ignoring constantly changing phonological information and if they can use the resulting information to facilitate voice change detection. Further, the study aimed at understanding whether the use of abstraction is restricted to the speech domain or can be deployed also in non‐speech contexts. We ran an electroencephalogram (EEG) experiment including one passive and one active oddball task, each featuring a speech and a rotated speech condition. In the speech condition, participants heard constantly changing vowels uttered by a male speaker (standard stimuli) which were infrequently replaced by vowels uttered by a female speaker with higher pitch (deviant stimuli). In the rotated speech condition, participants heard rotated vowels, in which the natural formant structure of speech was disrupted. In the passive task, the mismatch negativity was elicited after the presentation of the deviant voice in both conditions, indicating that listeners could successfully group together different stimuli into a formant‐invariant voice representation. In the active task, participants showed shorter reaction times (RTs), higher accuracy and a larger P3b in the speech condition with respect to the rotated speech condition. Results showed that whereas at a pre‐attentive level the cognitive system can track pitch regularities while presumably ignoring constantly changing formant information both in speech and in rotated speech, at an attentive level the use of such information is facilitated for speech. This facilitation was also testified by a stronger synchronisation in the theta band (4–7 Hz), potentially pointing towards differences in encoding/retrieval processes.

Developmental dyslexia (DD) affects approximately 10% of individuals, impairing reading ability thus limiting professional fulfilment and psychological wellbeing. DD is associated with both phonological and visual deficits, and the latter are attributed to dysfunctions of the magnocellular-dorsal visual stream, which has a critical role in planning saccades and supporting the extraction of letters/words identity. Currently, there are no effective treatments to restore the brain networks underlying visuospatial analysis and oculomotor efficiency. Adults with DD were enrolled in a randomised clinical trial introducing a non-invasive neuromodulation protocol specifically designed to enhance dorsal stream functionality. We used bi-focal beta-band transcranial alternating current stimulation (tACS) in parietal areas, due to the recognized role of beta oscillation in the dorsal stream functionality. Coupled with a 12-session visuoattentional training, such protocol induced improvements in reading speed, oculomotor control, and visual motion perception. Additionally, beta-tACS led to long-term enhancement of working memory. These outcomes were exclusive or superior to those obtained with a placebo/sham neuromodulation, and were accompanied by plastic changes in the stimulated brain networks. Overall, our findings show the efficacy of multisession tACS in improving core visual, oculomotor and cognitive deficits associated with reading disorders.

The temporal relationship between incoming signals is crucial in determining whether multisensory information is integrated into unitary percepts. Temporal binding windows (TBWs) define the time range within which multisensory inputs are highly likely to be perceptually integrated, even if asynchronous. TBWs widen with stimulus complexity and neurodevelopmental conditions (e.g., autism and schizophrenia), yet the key factors underlying their malleability remain unclear. The (quasi)rhythmic properties of sensory inputs, frequently embedded in natural stimuli (e.g., speech), are among the possible exogenous modulators. Indeed, stimulus spectral features can influence the alignment of neural excitability across sensory regions, synchronizing brain rhythms with external rhythmic patterns through phase‐reset mechanisms and neural entrainment. In a series of psychophysical studies, we presented simultaneity judgement tasks with pulsing audio‐visual (AV) streams amplitude‐modulated according to different regular frequencies or following purely rhythmic vs. quasi‐rhythmic (speech‐like) envelopes. Results show that TBWs decrease as the stimulus frequency increases and that speech‐like streams are integrated across larger TBWs. These findings highlight the importance of stimulus spectral structure in shaping multisensory perception. Furthermore, they show that quasi‐rhythmic spectrotemporal features of speech‐like streams induce more tolerant cross‐modal temporal processing even when the leading stimulation frequency is controlled for, putatively reflecting an adaptation to the variable rhythmic structure of natural speech. Our results align with neurophysiological accounts of neural entrainment and motivate future research in clinical populations with multisensory processing deficits.