Bangel, K. A. | Search bioRxiv

bioRxiv2017

Aberrant brain response after auditory deviance in PTSD compared to trauma controls: An EEG study.

Part of the symptomatology of post-traumatic stress disorder (PTSD) are alterations in arousal and reactivity which could be related to a maladaptive increase in the automated sensory change detection system of the brain. In the current EEG study we investigated whether the brains response to a simple auditory sensory change was altered in patients with PTSD relative to trauma-exposed matched controls who did not develop the disorder. Thirteen male PTSD patients and trauma-exposed controls matched for age and educational level were presented regular auditory pure tones (1000 Hz, 200 ms duration), with 11% of the tones deviating in both duration (50 ms) and frequency (1200 Hz) while watching a silent movie. Relative to the controls, patients who had developed PTSD showed enhanced mismatch negativity (MMN), increased theta power (5-7 Hz), and stronger suppression of upper alpha activity (13-15 Hz) after deviant vs. standard tones. Behaviourally, the alpha suppression in PTSD correlated with decreased spatial working memory performance suggesting it might reflect enhanced stimulus-feature representations in auditory memory. These results taken together suggest that PTSD patients and trauma-exposed controls can be distinguished by enhanced involuntary attention to changes in sensory patterns.

neuroscience↗

bioRxiv2017

Expect to neglect: Cross-modal resource allocation in anticipation of visual load

Human information processing is limited in capacity. To prevent sensory overload, expectation of upcoming events has been suggested to allocate processing resources to task-relevant regions (e.g., visual system), at the expense of processing in task-irrelevant regions (e.g., auditory system). In support of this, for tasks involving a high visual perceptual load (e.g. visual target search within physically similar distractors), auditory evoked responses were found to be attenuated1. This EEG study aimed to further elucidate the neural mechanisms by which the brain prepares for sensory overload. We investigated how expectancy about visual load modulated neural activity, prior to the onset of visual stimuli. Visual load in a letter search task was manipulated by varying the target letters similarity to the remaining letters and the letter set size from which flankers were randomly drawn. Importantly, audio-visual cues signaled the likely visual load of the upcoming stimulus-array, manipulating expectancy about visual task load. Cues signaling high visual load elicited attenuated auditory-evoked responses and increased alpha activity over task-irrelevant (auditory) regions, suggesting a functional inhibition of those regions already prior to the arrival of the visual array to suppress auditory cue processing. We also observed a sustained posterior positivity in the ERPs after high perceptual load cues, whose amplitude correlated with reaction times, suggestive of resource allocation for the upcoming visual targets. Expectation about visual load may thus prepare the attentional system both by facilitating target processing and task execution and inhibiting irrelevant sensory processing, thus providing efficient means to overcome attentional limits in situations with complex visual input.

neuroscience↗