Cold exposure enhances visual responses in human cortex

Transient changes in global physiological state caused by single acute exposures to stress can modulate different stages of information processing in the human brain. In some tasks there is evidence of enhanced sensory processing (Phelps et al., 2006), while in others there is evidence of impairments at later stages of information processing (Shackman et al., 2006). Here, we tested the effect of repeated cold exposure on multiple stages of information processing measured within a single task. Participants (n=40) completed a three-stimulus oddball task presented at fixation and overlaid upon a large, task-irrelevant, contrast-reversing circular checkerboard (8.57Hz). Participants responded to rare target stimuli (p=0.1) and ignored standards (p=0.8) and distractors (p=0.1). Participants completed the task before, during, and after a cold pressor test (CPT), where both feet were immersed in a bucket of ice-water (~4˚C; 90s). They completed five rounds of this protocol while brain activity was measured using electroencephalography (EEG), and pupil size, eye position, and psychophysiological responses were continuously recorded. Response times to target stimuli were faster during-CPT compared to pre- and post-CPT (p<.001). The amplitude of the steady-state visually evoked potential (SSVEP) associated with the task-irrelevant checkerboard stimulation frequency was higher during-CPT and post-CPT compared to pre-CPT (p<.01), suggesting that sensory evoked responses are modulated by cold exposure. Target evoked responses (P3 ERP amplitude and latency) were not modulated by the CPT (p>0.05), suggesting later stage processes associated with target recognition are not modulated by cold exposure. These data suggest that acute exposure to a noxious stressor can selectively enhance different stages of information processing.