Final Report Summary - ALERT AND FOCUSED (Arousal, cortical signal-to-noise, and the ability to sustain attention)
1. PUBLISHABLE SUMMARY
Sustained attention or the ability to maintain an alert, goal-directed focus is critical for many levels of human behavior. Failures of sustained attention occur when there is a transient decrease in endogenous control of behavior leaving one prone to goal-neglect and distraction by irrelevant stimuli. Frequent lapses in sustained attention are a core feature of performance in the elderly, sleep-deprived individuals, and patients with brain injury and mental disorders with attentional components, such as attention-deficit hyperactivity disorder and schizophrenia. Even healthy individuals differ substantially in their ability to sustain attention. An important question therefore concerns the brain mechanisms that give rise to deficits in sustained attention. The aim of this research project was to study the neural mechanisms underlying the ability to maintain an alert, goal-directed focus, and the effects of an alertness training on this ability.
One key hypothesis was that decrements in performance typically observed when people do a task for a prolonged period of time reflect reductions in the stability of cortical signals (or enhanced cortical ‘noise’) and that these are related to decreases in arousal. In a first study, we used electroencephalography (EEG) and skin conductance response (SCR) measurements to examine what happens neurally when subjects perform a sustained attention task for a prolonged period of time (80 minutes) without breaks, in relationship to changes in arousal. 32 subjects participated in the study. Our main prediction was that with time on task, performance would deteriorate and that this reduction in performance would be accompanied by reductions in arousal and cortical signal stability over frontal regions. To ensure that any changes observed at the level of behavior or the brain did not simply reflect reduced motivation with time on task, subjects were presented with an unexpected monetary incentive 60 minutes into the task aimed at motivating them to do their utmost best during the last 20 minutes of the task. We expected that this motivation manipulation would not be able to revive performance to initial levels.
Results showed that, as expected, with time on task, performance on the attention task rapidly declined (Figure 1A; p=.001). Subjects more often missed target events and they became slower to react. Notably, this decrement in performance was accompanied by changes in brain activity as measured with EEG. Specifically, as predicted, brain responses to stimuli became more variable with time on task, as indexed by theta-band phase consistency 150-500ms post-stimulus, indicating reduced attentional stability or focus (p=.002). This change in cortical signal stability occurred over frontal and occipital scalp regions (Figure 1B) and closely mirrored the observed behavioral decrement in performance (Figure 1C). The motivation manipulation improved both behavioral and neural performance, but only partially and transiently (Figures 1A and C). Contrary to our prediction, no significant associations were observed between arousal as measured by SCR and observed changes in attentional stability and performance. Together, these findings indicate that reductions in the ability to sustain attention after prolonged task performance are associated with more variable brain responding to important events. As motivation alone was not sufficient to reverse this time on task effect, prolonged task performance may deplete limited cognitive control resources.
Another notable, albeit unexpected, finding of the current project was that sustained attention to one location in space for 80 minutes led to completely lateralized early stimulus-evoked ERP components As can be seen Figure 2, the early evoked P1 and
[See attached document]
Figure 1. (A) This figure shows that with time on task, the ability to dissociate target from non-target stimuli (as indexed by A’ or perceptual sensitivity) rapidly declined, and furthermore, that motivation increases alone were not sufficient to reverse this performance decrement. The monetary incentive was introduced after block 6. Notably, the observed changes in performance were tightly coupled to changes in neural signal stability, as indexed by theta phase consistency, over frontal and occipital brain regions (B and C).
N1 components were completely lateralized to ipsilateral and contralateral posterior scalp regions. This finding is in striking contrast to previous studies which typically observed bilateral attentional modulations of early sensory processing when subjects alternated between attending left and right, and substantiates the idea that the P1 reflects inhibition and the N1 amplification. Of further note, the fact that these early potentials only occurred over one hemisphere indicates that they may not reflect exogenous sensory signals, as generally assumed, but top-down modulations of feed-forward sensory processing. These findings highlight the influence of statistical task structure and predictions on attentional control dynamics and stimulus processing. Follow-up studies are conducted to further explore the relationship between attention and prediction.
[See attached document]
Figure 2. The early evoked components (P1 and N1) were completely lateralized to, respectively, ipsilateral and contralateral posterior occipital cortex (POC).
Together, the first findings from this project link deficits in sustaining attention to less stable cortical signals in particular in frontal and visual brain areas. These findings have informed subsequent studies examining the precise neural networks and neurochemical mechanisms underlying attention. We anticipate that the results from this project will enhance our understanding of the mechanisms underlying our ability to maintain an alert, goal-directed focus, and provide an important basis for future research in the clinical and educational domain.
Sustained attention or the ability to maintain an alert, goal-directed focus is critical for many levels of human behavior. Failures of sustained attention occur when there is a transient decrease in endogenous control of behavior leaving one prone to goal-neglect and distraction by irrelevant stimuli. Frequent lapses in sustained attention are a core feature of performance in the elderly, sleep-deprived individuals, and patients with brain injury and mental disorders with attentional components, such as attention-deficit hyperactivity disorder and schizophrenia. Even healthy individuals differ substantially in their ability to sustain attention. An important question therefore concerns the brain mechanisms that give rise to deficits in sustained attention. The aim of this research project was to study the neural mechanisms underlying the ability to maintain an alert, goal-directed focus, and the effects of an alertness training on this ability.
One key hypothesis was that decrements in performance typically observed when people do a task for a prolonged period of time reflect reductions in the stability of cortical signals (or enhanced cortical ‘noise’) and that these are related to decreases in arousal. In a first study, we used electroencephalography (EEG) and skin conductance response (SCR) measurements to examine what happens neurally when subjects perform a sustained attention task for a prolonged period of time (80 minutes) without breaks, in relationship to changes in arousal. 32 subjects participated in the study. Our main prediction was that with time on task, performance would deteriorate and that this reduction in performance would be accompanied by reductions in arousal and cortical signal stability over frontal regions. To ensure that any changes observed at the level of behavior or the brain did not simply reflect reduced motivation with time on task, subjects were presented with an unexpected monetary incentive 60 minutes into the task aimed at motivating them to do their utmost best during the last 20 minutes of the task. We expected that this motivation manipulation would not be able to revive performance to initial levels.
Results showed that, as expected, with time on task, performance on the attention task rapidly declined (Figure 1A; p=.001). Subjects more often missed target events and they became slower to react. Notably, this decrement in performance was accompanied by changes in brain activity as measured with EEG. Specifically, as predicted, brain responses to stimuli became more variable with time on task, as indexed by theta-band phase consistency 150-500ms post-stimulus, indicating reduced attentional stability or focus (p=.002). This change in cortical signal stability occurred over frontal and occipital scalp regions (Figure 1B) and closely mirrored the observed behavioral decrement in performance (Figure 1C). The motivation manipulation improved both behavioral and neural performance, but only partially and transiently (Figures 1A and C). Contrary to our prediction, no significant associations were observed between arousal as measured by SCR and observed changes in attentional stability and performance. Together, these findings indicate that reductions in the ability to sustain attention after prolonged task performance are associated with more variable brain responding to important events. As motivation alone was not sufficient to reverse this time on task effect, prolonged task performance may deplete limited cognitive control resources.
Another notable, albeit unexpected, finding of the current project was that sustained attention to one location in space for 80 minutes led to completely lateralized early stimulus-evoked ERP components As can be seen Figure 2, the early evoked P1 and
[See attached document]
Figure 1. (A) This figure shows that with time on task, the ability to dissociate target from non-target stimuli (as indexed by A’ or perceptual sensitivity) rapidly declined, and furthermore, that motivation increases alone were not sufficient to reverse this performance decrement. The monetary incentive was introduced after block 6. Notably, the observed changes in performance were tightly coupled to changes in neural signal stability, as indexed by theta phase consistency, over frontal and occipital brain regions (B and C).
N1 components were completely lateralized to ipsilateral and contralateral posterior scalp regions. This finding is in striking contrast to previous studies which typically observed bilateral attentional modulations of early sensory processing when subjects alternated between attending left and right, and substantiates the idea that the P1 reflects inhibition and the N1 amplification. Of further note, the fact that these early potentials only occurred over one hemisphere indicates that they may not reflect exogenous sensory signals, as generally assumed, but top-down modulations of feed-forward sensory processing. These findings highlight the influence of statistical task structure and predictions on attentional control dynamics and stimulus processing. Follow-up studies are conducted to further explore the relationship between attention and prediction.
[See attached document]
Figure 2. The early evoked components (P1 and N1) were completely lateralized to, respectively, ipsilateral and contralateral posterior occipital cortex (POC).
Together, the first findings from this project link deficits in sustaining attention to less stable cortical signals in particular in frontal and visual brain areas. These findings have informed subsequent studies examining the precise neural networks and neurochemical mechanisms underlying attention. We anticipate that the results from this project will enhance our understanding of the mechanisms underlying our ability to maintain an alert, goal-directed focus, and provide an important basis for future research in the clinical and educational domain.