Circadian misalignment alters resting-state functional connectivity of the salience network in rotating shift workers

STUDY OBJECTIVES

This study compared resting-state functional connectivity (rsFC) of the salience network (SN) between rotating shift workers (RSWs) and controls. Furthermore, we examined whether rsFC of the SN was correlated with sleep, emotion, cognition, and attention.

METHODS

The 60 RSWs and 57 controls enrolled in this study completed self-report questionnaires and sleep diaries to assess subjective sleep quality, and polysomnography and actigraphy to evaluate objective sleep and 24-hour rest-activity rhythm parameters. The participants also underwent resting-state functional magnetic resonance imaging and structural T1 scans. We performed a seed-based rsFC analysis of the SN using the anterior cingulate cortex (ACC) and anterior insula (AI) as seed regions. Furthermore, AI and ACC rsFC were compared in RSWs and controls, and we analyzed correlations between rsFC and variables of interest showing significant group differences.

RESULTS

Compared with controls, RSWs showed reduced rsFC between the ACC and right insula, and increased rsFC of the ACC with the left occipital lobe and right superior frontal gyrus extending to the supplementary motor area (SFG/SMA). Moreover, RSWs showed reduced rsFC between the right AI and right superior parietal lobule (SPL). Finally, rsFC between the ACC and right AI was correlated with 24-hour rest-activity rhythmicity.

CONCLUSIONS

Although RSWs did not show sleep disturbance, emotional distress, cognitive impairment, or attention deficits, alterations of right insula, left occipital lobe, right SFG/SMA, and right SPL rsFC in the SN indicate that impairments in salience detection and top-down attentional control may emerge in shift workers over time.

The visual-attention span deficit in developmental dyslexia: Review of evidence for a visual-attention-based deficit

The visual attention span (VAS) deficit hypothesis in developmental dyslexia posits that a subset of dyslexic individuals shows a multielement parallel processing deficit due to reduced visual attention capacity. However, the attention-based interpretation of poor performance on VAS tasks is hotly debated. The purpose of the present paper is to clarify this issue through a critical review of relevant behavioural and neurobiological findings. We first examine the plausibility of alternative verbal interpretations of VAS performance, evaluating whether performance on VAS tasks might reflect verbal short-term memory, verbal coding or visual-to-verbal mapping skills. We then focus on the visual dimensions of VAS tasks to question whether VAS primarily reflects visuo-attentional rather than more basic visual skills. Scrutiny of the available behavioural and neurobiological findings not only points to a deficit of visual attention in dyslexic individuals with impaired VAS but further suggests a selective endogenous attentional system deficit that relates to atypical functioning of the brain dorsal attentional network. The overview clarifies the debate on what is being measured through VAS tasks and provides insights on how to interpret the VAS deficit in developmental dyslexia.

Frontal eye fields control attentional modulation of alpha and gamma oscillations in contralateral occipitoparietal cortex

Covertly directing visuospatial attention produces a frequency-specific modulation of neuronal oscillations in occipital and parietal cortices: anticipatory alpha (8-12 Hz) power decreases contralateral and increases ipsilateral to attention, whereas stimulus-induced gamma (>40 Hz) power is boosted contralaterally and attenuated ipsilaterally. These modulations must be under top-down control; however, the control mechanisms are not yet fully understood. Here we investigated the causal contribution of the human frontal eye field (FEF) by combining repetitive transcranial magnetic stimulation (TMS) with subsequent magnetoencephalography. Following inhibitory theta burst stimulation to the left FEF, right FEF, or vertex, participants performed a visual discrimination task requiring covert attention to either visual hemifield. Both left and right FEF TMS caused marked attenuation of alpha modulation in the occipitoparietal cortex. Notably, alpha modulation was consistently reduced in the hemisphere contralateral to stimulation, leaving the ipsilateral hemisphere relatively unaffected. Additionally, right FEF TMS enhanced gamma modulation in left visual cortex. Behaviorally, TMS caused a relative slowing of response times to targets contralateral to stimulation during the early task period. Our results suggest that left and right FEF are causally involved in the attentional top-down control of anticipatory alpha power in the contralateral visual system, whereas a right-hemispheric dominance seems to exist for control of stimulus-induced gamma power. These findings contrast the assumption of primarily intrahemispheric connectivity between FEF and parietal cortex, emphasizing the relevance of interhemispheric interactions. The contralaterality of effects may result from a transient functional reorganization of the dorsal attention network after inhibition of either FEF.