Thesis title: Conflict monitoring and response inhibition: NIBS approach for exploring the functional contribution of the frontal and the occipito-temporal cortices in cognitive control
The thesis discusses the role of prefrontal and occipital brain areas in sustaining high cognitive functions during cognitive control. In particular, by using non-invasive repetitive Transcranial Magnetic Stimulation (rTMS), I explored how and to what extent cortical networks are causally involved in processing and monitoring motor-perceptual conflicts. For this purpose, different samples of healthy participants have been recruited to perform variants of the Eriksen Flanker and Go-NoGo Tasks while receiving rTMS in within-subject designs.
In Chapter 1, a narrative mini-review of transcranial electrical (tES) studies investigating conflict and error monitoring is presented. A special focus is supplied on how transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) can be delivered to modulate the performance monitoring network in neurotypical samples. Emphasis is given to studies targeting mid-frontal brain regions (such as the medial frontal cortex, MFC; and the dorsal anterior cingulate cortex, dACC) and to the functional role of exogenous theta oscillations in altering behaviour during the resolution of tasks tapping top-down control like the Stroop, the Flanker, and the Simon tasks.
In Chapter 2, it is presented a rTMS study that aims at providing causal spatial-temporal information on the neural computations underlying the processing of conflicting body-related stimuli. The purposes of this study were to: (i) investigate the functional pivotal role of the dorsomedial Prefrontal Cortex (dmPFC) in processing representational conflicts and behavioural errors during the Flanker task performance, and (ii) to elucidate the role of the right Extrastriate Body Area (rEBA) in perceptually supporting cognitive control processes. In turn, a 10Hz rTMS protocol was adopted during the resolution of a classical and modified version of the Eriksen Flanker task with stimuli representing either letters or human whole-body silhouettes. The results show a context-specific performance modulation associated with rEBA stimulation and lower accuracy in body trials, particularly among the underweight bodies versus overweight ones. Since modulation is particularly present in congruent trials, it can be assumed that increased cognitive control recruitment could mitigate the effects of stimulation on EBA.
Finally, in Chapter 3, it was probed the causal role of right Inferior Frontal Gyrus (rIFG) in response inhibition during different conditions of cognitive interference. The study also aims to better understand the causal role of rEBA in supporting the frontal cognitive network during response inhibition and response conflict, in case of involvement of body related stimuli. Past literature has already shown the crucial role of rIFG in restraining automatic responses and reported that such ability might be related to the degree of response competition and cognitive interference. Here the interaction between inhibitory function and conflict monitoring was investigated by delivering on-line 10Hz rTMS either on rIFG or rEBA during two variants of a Go/NoGo Flanker task, with stimuli representing letters (classical variant) or hands (body related variant). The results seem to confirm the role of rIFG in the inhibitory process, regardless of the content of the stimulus, in the size of reaction times of false alarms, increased during the stimulation of this area compared to the stimulation condition on rEBA. A side effect of the inhibitory alteration due to TMS on rIFG is observed in the dimension of the congruent GO trials’ reaction times and reduction of Flanker effect in the same dimension.
Taken together, the results of the two studies broaden the knowledge on the different contribution of frontal and occipital areas in different aspects of cognitive control e.g. conflict monitoring and inhibition of response, and pave the way for future investigations that effectively explore the existence of a functional relationship between the frontal control system and the body’s occipito-temporal network.