Soekadar, SurjoAndrade, Alexandre da Rocha Freire de, 1971-Carneiro, Teresa Meireles2024-03-192024-03-1920242023http://hdl.handle.net/10451/63498Tese de mestrado, Engenharia Biomédica e Biofísica , 2023, Universidade de Lisboa, Faculdade de CiênciasApproximately half of the world’s population suffers from neurological or neuropsychiatric disorders, often characterized by abnormal brain oscillations. Transcranial alternating current stimulation (tACS) has emerged as a prominent tool to modulate these brain oscillations and restore their normal patterns. This dissertation explores closed-loop amplitude modulated transcranial alternating current stimulation (CLAM-tACS), a novel technique developed to overcome phase-dependent effects typically produced by conventional tACS. Unlike conventional tACS, CLAM-tACS enables real-time adjustment of stimulation parameters, allowing for controlled phase-dependent stimulation. CLAM-tACS recently demonstrated effectiveness in modulating brain oscillations during stimulation, by varying the phase difference between stimulation and ongoing brain oscillations. However, it remains unknown whether these phase-dependent effects persist beyond stimulation. This study aimed to establish the consistency and duration of CLAM-tACS’s phase-dependent effects, along with their impact on behaviour. Ten healthy participants received CLAM-tACS targeting alpha oscillations over the occipitoparietal lobes, with simultaneous electroencephalography recording, while performing a working memory (WM) task. Participants were divided into two groups: one received stimulation with a target phase difference, 𝜑, of 0° between stimulation and alpha oscillations (𝜑 = 0° group), and the other with a 180° phase difference (𝜑 = 180° group). This dissertation’s hypothesis anticipated enhanced alpha oscillations in the 𝜑 = 0° group and suppressed alpha oscillations in the 𝜑 = 180° group, persisting beyond stimulation, and correlating with improved or decreased WM accuracy, respectively. Phase-lag index assessed physiological effects, while WM accuracy quantified behavioural changes. The Pearson correlation coefficient assessed the relationship between both. This study findings suggest that the 𝜑 = 180° group had enhanced alpha oscillations, but decreased WM accuracy, contradicting this dissertation’s hypotheses. Nevertheless, statistical tests found no significant group differences, precluding meaningful conclusions. However, the change in frontoparietal connectivity under CLAM-tACS predicted WM accuracy changes, indicating a causal link between the two. Further research is required to establish CLAM-tACS for sustained modulation of brain oscillationsengEstimulação Transcraniana por Corrente AlternadaCircuito FechadoOscilações AlfaConectividadeEletroencefalografiaTeses de mestrado - 2024master thesis203881427