The association between suicidal behavior, attentional control, and frontal asymmetry

It can be difficult to identify those at risk of suicide because suicidal thoughts are often internalized and not shared with others. Yet to prevent suicide attempts it is crucial to identify suicidal thoughts and actions at an early stage. Past studies have suggested that deficits in attentional control are associated with suicide, with the argument that individuals are unable to inhibit negative thoughts and direct resources away from negative information. The current study aimed to investigate the association of suicidal behavior with neurological and behavioral markers, measuring attentional bias and inhibition in two Stroop tasks. Fifty-four participants responded to the color of color words in a standard Stroop task and the color of positive, negative, and neutral words in an emotional Stroop task. Electroencephalographic (EEG) activity was recorded from frontal areas during each task and at resting. Participants were separated into a low-risk and high-risk group according to their self-20 reported suicidal behavior. Participants in the high-risk group showed slower response times in the color Stroop and reduced accuracy to incongruent trials, but faster response times in the emotional Stroop task. Response times to the word “suicide” were significantly slower for the high-risk group. This indicates an attentional bias towards specific negative stimuli and difficulties inhibiting information for those with high levels of suicidal behavior. In the emotional Stroop task the high-risk group showed reduced activity in leftward frontal areas, suggesting limitations in the ability to regulate emotional processing via the left frontal regions. The findings support the argument that deficits in attentional control are related to suicidal behavior. The research also suggests that under certain conditions frontal asymmetry may be associated with suicidal behavior

Using meditation to improve measures of attention in older adults

Age-related cognitive decline greatly impacts quality of life for older adults. Previous research has indicated that meditation may act as a neuroprotective factor to prevent age-related cognitive decline. This thesis sought to replicate previous findings and investigate if a four-week meditation intervention would improve sustained attention. Participants 60 years and older (n=27, 17 female) were recruited and assigned to a focused-attention (FA) meditation or relaxation group which met for four weeks, three times a week. Resting-state EEG was used to collect individual alpha peak frequency (iAPF) and frontal alpha asymmetry (FAA). The Sustained Attention to Response Task (SART) was also used to measure attention. After the intervention, we found no change in iAPF, FAA or SART performance. This thesis found that a four-week FA meditation practice does not influence sustained attention in older adults, however suggestions as to why no relationship was found are discussed and future research is warranted

How Life Experience Shapes Cognitive Control Strategies: The Case of Air Traffic Control Training

Although human flexible behavior relies on cognitive control, it would be implausible to assume that there is only one, general mode of cognitive control strategy adopted by all individuals. For instance, different reliance on proactive versus reactive control strategies could explain inter-individual variability. In particular, specific life experiences, like a highly demanding training for future Air Traffic Controllers (ATCs), could modulate cognitive control functions. A group of ATC trainees and a matched group of university students were tested longitudinally on task-switching and Stroop paradigms that allowed us to measure indices of cognitive control. The results showed that the ATCs, with respect to the control group, had substantially smaller mixing costs during long cue-target intervals (CTI) and a reduced Stroop interference effect. However, this advantage was present also prior to the training phase. Being more capable in managing multiple task sets and less distracted by interfering events suggests a more efficient selection and maintenance of task relevant information as an inherent characteristic of the ATC group, associated with proactive control. Critically, the training that the ATCs underwent improved their accuracy in general and reduced response time switching costs during short CTIs only. These results indicate a training-induced change in reactive control, which is described as a transient process in charge of stimulus-driven task detection and resolution. This experience-based enhancement of reactive control strategy denotes how cognitive control and executive functions in general can be shaped by real-life training and underlines the importance of experience in explaining inter-individual variability in cognitive functioning

Combined optogenetic and pharmacological analysis of 5-HT control of cortical microcircuitry

5-HT (5-hydroxytryptamine, serotonin) powerfully influences cognition and mood regulation. In the medial prefrontal cortex (mPFC), the intricate balance between excitation and inhibition in celluar microcircuits allow the generation of network oscillations that encode behaviour and cognition. In particular, parvalbumin expressing interneurons (PVINs) act as key regulators of the excitatory/inhibitory balance. The precise interactions between the 5-HT system and these PVINs, however, are little understood. Using an array of modern neuroscience tools, this thesis provides a comprehensive report of interactions between the 5-HT system and different neuron subtypes in the mPFC, including PVINs. In slice electrophysiology experiments, local application of 5-HT greatly increased the intrinsic excitability of genetically labelled PVINs in the mPFC via the 5-HT2A receptor. Such 5-HT2A receptor-mediated activation of PVINs was then demonstrated in in vivo silicon probe multi-unit recordings following the systemic administration of the 5-HT2A receptor agonists DOI and psilocin. Pharmacological activation of the 5-HT2A receptor suppressed slow wave oscillations and elevated multi-unit activity in the mPFC, possibly via the excitation of putative PVINs and the disruption of their correlated activity with neighbouring neurons. With an optogenetic approach, the effects of physiologically evoked 5-HT on neural activity in the mPFC were determined. This methodology was first verified with immunohistochemistry as well as in vitro and in vivo electrophysiology, which revealed diverse firing properties of optotagged 5-HT neurons. Specifically, optotagged regular-firing 5-HT neurons tended to fire action potentials following light stimuli up to 20 Hz, whereas optotagged irregular-firing 5-HT neurons were unlikely to sustain spiking at higher frequencies. Optogenetic activation of 5-HT neurons induced frequency-dependent suppression of slow wave oscillations and increase in UP state duration. Changes in the firing rate of individual neurons, including PVINs, were mainly inhibitory, although excitatory effects and non responders were also observed. Notably, optogenetic activation of 5-HT neurons at high frequencies disrupted the spiking correlation between putative PVINs and other neurons, once again providing a potential mechanism for 5-HT modulation of excitatory-inhibitory balance and local oscillations in the mPFC. Collectively, this thesis presents concrete evidence for 5-HT modulation of microcircuit activity, including PVINs, in the mPFC. These findings highlight the importance of elucidating the actions of 5-HT on a cellular level in gaining a better understanding of how 5-HT shapes cortical network output and, ultimately, cognition