Sleep-Like Slow Waves Modulate Attention While Awake
Post by Lincoln Tracy
The takeaway
Increases in sleep-like slow wave activity, while we are awake, could explain why we find it hard to sustain attention to something over an extended period of time.
What's the science?
Our ability to sustain attention to a specific task is determined by our level of physiological arousal. Paying attention to a specific thing for an extended period is challenging, and often results in our minds starting to wander. Several neurotransmitters – including noradrenaline, dopamine, and serotonin – modulate both physiological arousal and sustained attention. Electrophysiological markers – brain activity recorded on an electroencephalogram (EEG) – are commonly used to explore the relationship between physiological arousal and attention. Although lapses in sustained attention and dysregulations in arousal have been linked, the physiological mechanisms underlying these associations are unknown. This week in the Journal of Neuroscience, Pinggal and colleagues aimed to explore the relationship between the occurrence of sleep-like slow brain waves and the behavioral consequences of sustained attention failures by pharmacologically manipulating noradrenaline, dopamine, and serotonin levels in a cohort of healthy male participants.
How did they do it?
The authors undertook a secondary analysis of data previously collected from 32 healthy, young right-handed males as part of a four-arm, randomized, placebo-controlled trial. Over four experimental testing sessions, participants were administered methylphenidate (to raise noradrenaline and dopamine levels throughout the brain), atomoxetine (to raise noradrenaline and dopamine levels specifically in the prefrontal cortex), citalopram (to raise serotonin levels), or placebo (as a control) before donning an EEG cap and completing an experimental task which measures sustained attention. As part of the task, participants were presented with a series of pictures presented for just under a second (short trial) or just over a second (long trial). They were instructed to respond (by pressing a computer key) when the picture was presented for the longer period. The authors recorded the proportion of missed targets (when the participant failed to press the key on a long trial) and false alarms (when the participant pressed the key on a short trial), as well as the reaction time for correct responses to the long trials. Sleep-like slow wave activity was recorded throughout the task. Behavioral performance and EEG data after administration of each of the drugs were compared to placebo.
What did they find?
The authors found methylphenidate improved behavioral performance on all measures compared to placebo. This means after taking methylphenidate, participants were faster and better at identifying the long trials, without becoming too overreactive and responding to short trials. In contrast, atomoxetine increased false alarms, and citalopram increased missed long trials. Therefore, the three drugs had unique effects on behavioral performance. With respect to the EEG data, citalopram increased sleep-like slow wave density during the sustained attention task compared to placebo when data from all electrodes were averaged, while methylphenidate and atomoxetine did not affect brain activity. When sleep-like slow wave density was examined across the individual electrodes (to examine how the drugs affected slow wave density in different parts of the brain), citalopram resulted in a widespread increase in density across different regions, while methylphenidate and atomoxetine reduced sleep-like slow wave density in central and frontal brain regions.
What's the impact?
This study found that optimal performance on a sustained attention task requires a delicate balance between activation and inhibition, impulsivity, and sluggishness. Importantly, this delicate balance is achieved through synergistic interactions of multiple neurotransmitters. These findings reinforce the idea that behavioral impairments that occur in disorders such as ADHD may occur through the dysregulation of arousal.