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Assessing the Aftereffects of Closed-Loop Amplitude Modulated Transcranial Alternating Current Stimulation on Parieto-Occipital Alpha Oscillations
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Resumo(s)
Approximately 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 oscillations
Descrição
Tese de mestrado, Engenharia Biomédica e Biofísica , 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Estimulação Transcraniana por Corrente Alternada Circuito Fechado Oscilações Alfa Conectividade Eletroencefalografia Teses de mestrado - 2024