Electrophysiological correlates of response inhibition and error processing: The effects of strategic manipulation, feedback and traumatic brain injury

Three studies examined the executive functions of sustained attention, behavioral monitoring, response inhibition, and error processing and how these are affected by traumatic brain injury (TBI). All studies used a Go-Nogo task (1) that heavily taxes response-inhibition and monitoring with the use of an improbable Nogo stimulus and constant SOA, and (2) has been found to result in abnormally high error rates in TBI patients. Behavioural and event-related potential (ERP; recorded at 47 electrodes) measures were collected. First, the physiological processes in healthy, young adults were outlined. The predominant “rhythmic” response mode is controlled by the visual stimulus and time-estimation from the preceding response (negative frontal slow wave, FSW). The recognition of the Nogo stimulus is indicated by the posterior N225 that prompts response. The conscious recognition of this inhibition is represented by the fronto-central N300. These processes can be modulated by two feedback mechanisms that serve to “break” the rhythm: (1) monitoring of event-probabilities, P500, and (2) monitoring of errors, Ne/Pe complex. Next, the disordered processes in TBI patients were delineated. The TBI group made more errors than the Control group. The TBI group failed to show the response-related effect in the left frontal region, suggesting deficits in the conscious monitoring of response tendencies. The N300 on Correct Withhold trials was reduced or delayed in the TBI group. In addition, the Ne component (error-detection) was reduced in a group of relatively “acute” TBI patients, while the Pe component (post-detection error processing) was reduced in a group of chronic TBI patients. Finally, because errors can be predicted by RT speed-up, participants were given (a) strategic instructions to slow down, and (b) external feedback (FB) when RTs became to fast. Errors were reduced in the TBI group with strategic instructions and this improvement was maintained by the external FB. ERPs indicated enhanced processing of Speed-FB tones compared to baseline. The Go Response N300, associated with tonic inhibition across all trials, increased with improvements in performance. However, there were no changes in the FSW or the Ne/Pe with these improvements. Improved performance following TBI can be achieved by deliberate slowing facilitated through feedback.