The role of the frontal lobe in attention and conscious perception processes in healthy population and patients with acquired brain injury

Resumen

The main aim of this thesis was to address the role of the frontal lobe in the control of attention. The first research line examined for the first time the behavioral and neural interactions between interference control aspect of the executive control attention network (elicited by a classic Stroop task) and the visual conscious perception of near-threshold stimuli. Results from the first experimental series showed a modulation of the decision criterion to respond to the near-threshold stimulus on incongruent as compared to congruent Stroop trials. This effect was associated to the transient recruitment of reactive control, as incongruent trials were also infrequent (high proportion congruent condition), and participants were more likely to adopt reactive control strategies (Braver, 2012). We hypothesized that the impact of interference control on decision stages of conscious processing was due to the implication of shared frontal regions in both conflict detection and conscious perception. To test this hypothesis, we conducted a second experimental series in which we employed high-density EEG in order to look at the neural bases of this behavioral interaction. In this study, the finding of an interference control modulation on the response criterion to the near-threshold stimulus was replicated, although in this experiment it was associated with proactive strategies of control, as it was observed on congruent and infrequent trials (low proportion congruent condition). Results of the event-related potentials (ERPs) analyses in this experiment showed a modulation of the conflict-related N2 component to the Stroop stimulus (Luck, 2012; Yeung, Botvinick, & Cohen, 2004) by the conscious perception of the near-threshold stimulus. This modulation was only observed on incongruent and infrequent trials in the high proportion congruent session (when reactive control mechanisms are recruited) and on congruent and infrequent trials in the low proportion congruent session (thought to recruit proactive control mechanisms), suggesting that, in addition to interference-related conflict, the N2 component and its modulation also reflected expectancy-related conflict (Luck, 2012; Yeung et al., 2004). The source-location analyses confirmed that, as expected, the N2 component was associated with activation of the anterior cingulate cortex. Therefore, the combination of behavioral and electroencephalography results from this line of research suggests a modulation of interference-related and expectancy-related conflict on the perceptual-decision aspect of conscious perception, due to the recruitment of frontal areas, likely involving the anterior cingulate cortex, on both conflict detection and the decisional stage of conscious perception. The second line of research of the present thesis explored attention processes and their neural substrates in the syndrome of confabulations after acquired brain injury, which is characterized by the unintentional (and unconscious) production of false memories (Dalla Barba, 1993), and usually involves lesions to the orbitofrontal cortex (Schnider, 2008). For the first time in the literature, we assessed confabulating patients’ performance in three experimental tasks measuring the three attention networks (Petersen & Posner, 2012) and we explored the association between patients’ performance on those tasks with grey matter and white matter damage. Results from this study showed that, when compared with lesion controls (matched non-confabulating patients) and healthy controls, confabulators showed an impairment of the executive network of attention, characterized both by a higher Simon interference effect and disinhibition in a Go-NoGo task. Coherent to previous studies, this disinhibition pattern was related to damage to the right inferior frontal cortex (Aron, Robbins, & Poldrack, 2014). In addition, confabulating patients showed a greater alertness task, which was associated with damage to the right anterior insula and putamen, structures related to sustained attention and task engagement-disengagement (Sridharan, Levitin, & Menon, 2008; Thakral & Slotnick, 2009). This data suggest that patients with lesions in the right anterior insula and putamen had deficits in sustained attention, and therefore greatly depended on phasic alertness cues to detect the subsequent target. Moreover, confabulating patients and lesion controls relied more on exogenous cues in the spatial orienting task than healthy controls, probably due to deficits in the ventral network of the reorienting of attention (Corbetta, Patel, & Shulman, 2008). In fact, lesions in our sample of patients mostly affected white matter pathways related to the ventral network of attention in the right hemisphere: the middle and ventral branches of the superior longitudinal fascicule (Thiebaut de Schotten et al., 2011). Coherent with previous studies in left unilateral neglect, the integrity of those white matter tracts positively correlated with our participants’ performance in the spatial orienting task (Bartolomeo, Thiebaut De Schotten, & Doricchi, 2007). Results from the neuropsychological assessment in our study are coherent with previous literature showing both memory and executive deficits in confabulating patients (Fischer, Alexander, D'esposito, & Otto, 1995; Stuss, Alexander, Lieberman, & Levine, 1978); however, we focused on further examining the attention deficits associated with confabulations after acquired brain damage. Our research supports recent findings highlighting the role of attention mechanisms in the production of confabulations (Ciaramelli, Ghetti, & Borsotti, 2009; Cunningham et al., 1997; Ródenas, Lupiáñez, Arnedo, & Triviño, 2016; Triviño, Ródenas, Lupiáñez, & Arnedo, 2017), and disentangles the attentional mechanisms impaired in the syndrome of confabulations.