Biology subjects

Bareham, C.

Publications and source records attributed to Bareham, C..

3 recordsLinked to original sources

bioRxiv2025

Effective connectivity reveals a shift to left-hemisphere dominance for spatial attention with diminishing arousal

Spatial attention becomes biased toward the right side of space when alertness wanes, but the neural mechanisms underlying this shift remain unresolved. Competing theories propose that spatial attention depends either on a dominant right hemisphere, interhemispheric competition, or interactions between dorsal and ventral attention networks. Here, we used drowsiness as a model to investigate how diminishing alertness reshapes the cortical dynamics supporting auditory spatial attention. Thirty healthy participants completed a lateralised auditory localisation task while high-density EEG was recorded during wakefulness and drowsiness. Behaviourally, drowsiness selectively impaired localisation accuracy for left-sided stimuli, replicating the typical neglect-like rightward attentional bias observed with lower arousal in healthy people, and pathological attention deficits in brain injury patients. Using Dynamic Causal Modelling and Parametric Empirical Bayes, we identified a striking reconfiguration of effective cortico-cortical connectivity across arousal states. During wakefulness, spatial attention was characterised by reciprocal interhemispheric signalling between inferior frontal regions, consistent with balanced bilateral coordination. During drowsiness, this pattern shifted toward reduced right frontoparietal connectivity together with increased left-hemispheric parietofrontal connectivity. These findings suggest that waning alertness destabilises balanced interhemispheric control and allows left-hemispheric processing to dominate attentional processing. Rather than fully supporting existing theories of spatial attention, our results point toward a hybrid mechanism in which neglect-like spatial bias emerges from the interaction between right-hemispheric dysconnection and left-hemispheric dominance under low arousal. Diminishing alertness reshapes interhemispheric coordination rather than simply reducing right-hemisphere function.

neuroscience↗

bioRxiv2023

Brain network dynamics in transitions of consciousness reorganize according to task engagement

Substantial changes in behavior, physiology, and brain function occur when alertness decreases 1- 5. These changes in brain function involve increased synchronization between cortical areas 6,7 as well as alterations in sensory processing pathways and networks connecting the thalamus and cortex 5,8-11. Cognitive tasks engage overlapping functional networks with sensory pathways facilitating information processing 12,13, and thalamocortical and corticocortical networks supporting task performance 14,15. Frontoparietal circuits play a crucial role in cognitive tasks 16 and states of decreased consciousness 17. To develop an integrated framework of consciousness and cognition, it is important to understand how fluctuations in alertness and cognitive processing interact in these shared circuits 18. Our hypothesis is that during periods of low alertness, individuals who actively maintain task engagement would recruit additional frontoparietal and sensory processing networks, while thalamocortical dynamics that typically change during sleep onset would remain unaffected. Our findings demonstrated that as alertness decreased, passively listening to auditory tones led to increased synchronization in the parietal lobe, whereas actively performing an auditory task resulted in increased long-range frontoparietal synchronization. During decreasing alertness, passive listening (but not active task engagement) was associated with widespread increased synchronization between the thalamus and cortex. In contrast, active task engagement (but not passive listening) led to increased synchronization between the auditory cortex and the rest of the brain. These results reveal the functional mechanisms of the brains flexible reorganization during transitions of consciousness when individuals are actively engaged in cognitive processes.

neuroscience↗

bioRxiv2023

Effects of alertness on perceptual detection and discrimination

The level of alertness fluctuates throughout the day, exerting modulatory effects on human cognitive processes at any moment. However, our knowledge of how alertness level interacts with specific cognitive demands and perceptual rules of the task is still limited. Here we use perceptual decision-making paradigms to understand how alertness modulates the detection of a stimulus and the capacity to discriminate one stimulus from another. We analyzed data from four different experiments (113 participants in total): 1 - auditory masking detection; 2 - sensorimotor detection; 3 - auditory spatial discrimination; and 4 - auditory phoneme discrimination, and examined the performance of participants during the natural transition from awake (high alertness) to drowsy (low alertness). First, we fitted psychometric functions to the hit rates across different conditions of difficulty for EEG-defined high and low alertness metastable states, respectively. Second, we performed modelling of slope and threshold for the fitted curves as well as signal detection theory measures of perceptual sensitivity (d) and response bias (criterion). We found lower detection and discrimination sensitivity to stimuli as alertness level decreases, signalled by a shallower slope of the sigmoidal curve and a lower d, while the threshold increases slightly and equivalently across experiments during lower alertness. There was no change in the criterion to make the decision during the transition. These results suggest that reduced alertness generally decreases the quality of perceptual decision-making. Zooming in, we observed that the decrease in sensitivity measured by slope was stronger for discrimination than for detection decisions, indicating that lower alertness impairs the precision of decisions in discriminating alternatives more than identifying the presence of a stimulus around the threshold. Taken together, these results suggest that alertness has a common effect on perceptual decision-making and differentially modulates detection and discrimination decisions.

animal behavior and cognition↗