EEG SIGNATURES OF PAIRED ASSOCIATES LEARNING AND THEIR MODULATION IN HEALTHY ADULTS AND PATIENTS WITH NEUROVASCULAR DISORDERS

Deficits in episodic, associative and working memory affect both normal and pathological aging. These deficits reflect alterations in distributed neural networks, including cortical circuits observable with scalp EEG. However, the EEG signatures of associative learning and their alteration in normal and pathological aging remain unclear, and evidence remains largely correlational.
Here, we designed a clinical study to investigate the EEG correlates of associative learning during a Paired Associates Learning task in healthy adults and patients with cognitive complaints associated with cerebral small vessel disease. We hypothesize that changes in the theta frequency band underlie performance on this task. Preliminary analysis of task-related spectro-temporal EEG dynamics indicate a pronounced parieto-occipital event-related potential following the presentation of visual stimuli during both encoding and recall. During recall, this ERP was occasionally followed by theta-band oscillations spanning prefrontal and parieto-occipital regions.
To probe the causal role of theta oscillations in memory, we applied theta range bifocal transcranial alternating current stimulation (tACS) to prefrontal and parietal cortices and measured effects on EEG and task performance. Stimulation parameters (electrodes montage and stimulation amplitude) were personalized using MRI-based simulations. Preliminary results show good tolerability by the subjects at amplitudes achieving ~0.25 V/m at target sites, corresponding to a 50% probability of eliciting minimal significant effects. Analysis of tACS effects on EEG and task performance is ongoing.
This study aims to clarify how aging and vascular brain alterations shape the neural dynamics of associative memory and to explore the potential of non-invasive brain stimulation to modulate these processes.