Cognitive energetic mechanisms and neural basis of alertness regulation
Human cognition is influenced by "energetic" factors like effort or fatigue. Interestingly, seemingly easy or well-practiced tasks that still require a continuous attentional engagement, have been found especially susceptible to the effects of such energetic variables. Particularly in monotonous and cognitively little challenging tasks, impaired performance, from reduced efficiency to catastrophic errors, often results from temporary deficits in sustaining attention. A classic paradigm with minimal cognitive demands that is used for examining the most basic form of sustained attention is simple reaction-time tasks. These tasks require a rapid motor response to predefined stimuli. The reaction upon stimulus detection is always the same, and the only unknown variable is the exact moment of stimulus occurrence. Attaining and maintaining a state of readiness to respond in such tasks has been termed "alertness." This thesis investigates cognitive-energetic mechanisms that contribute to alertness and its decrease over time as well as the neurobiological basis of alertness regulation. The first investigation (Study 1) examined in three 25-min simple reaction-time tasks, which posed different demands on attention via manipulations of stimulus salience, whether performance decrements with time on task can be better explained with increasing drifts of the attentional focus away from the task (distraction hypothesis) or with a depletion of attentional resources (mental-fatigue hypothesis). The performance and questionnaire data largely corroborated the latter explanation, since decrements and subjective fatigue increased more with higher attentional demands. The increase of self-reported task-unrelated thoughts over time, however, provided some evidence for the distraction hypothesis as well. Based on these findings, an approach is developed that incorporates both explanations in a hierarchical model of self-regulation. Study 2 examined the question as to what extent the mechanisms of temporal preparation under time uncertainty, which contribute to optimal performance in simple reaction-time tasks, suffer from exhaustion after prolonged continuous demands. In a 50-min simple reaction-time task, we found the typical reaction-time slowing with time on task but no change in parameters of temporal preparation (i.e. the so-called variable and sequential foreperiod effects, respectively). This suggests (a) that cognitive processes of temporal preparation do not significantly contribute to alertness decrements with time on task and (b) that the mechanisms underlying temporal preparation are processes that are hardly susceptible to mental fatigue, such as nonintentional associative learning. The third experiment (Study 3) investigated the brain network subserving alertness regulation - independent of the sensory modality of the response signals. We used functional magnetic resonance imaging to measure brain activity during simple reaction-time performance in tasks with auditory, tactile or visual stimuli. The results revealed a supramodal (i.e. modality-independent) brain network consisting of predominantly right-lateralized cortical areas as well as brainstem and cerebellar structures. This corroborates the modality independence of previous findings from single-modality studies that used positron emission tomography and demonstrates that the notion of a right-lateralized network for alertness regulation can be generalized to tactile stimuli. Taken together, the results of the thesis show that a variety of - fatigable as well as non-fatigable - processes contribute to maintaining response readiness in simple reaction-time tasks, which appear to be subserved by a widespread supramodal brain network. These findings raise the question for future research and application to what extent the construct "alertness" may be segregated into useful subcomponents to achieve a refined differentiation in diagnostic contexts.
info:eu-repo/classification/ddc/150, Neuropsychologie, Kognitive Psychologie, Bildgebendes Verfahren, Experimentelle Psychologie, Reaktionszeit, Psychologie, Aufmerksamkeit, funktionelle Kernspintomographie, Neuropsychology, Experimental Psychology, Neuroimaging, Attention, fMRI
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