Book Description

One of the core problems the brain has to solve is how to navigate and interact with the external world. This requires a complex analysis of sensory input, the translation of perceptual input to goal-directed behavior, followed by motor planning and execution. In this thesis we investigated two crucial aspects of this perception-action cycle. First, we examined the underlying neural mechanisms that support response inhibition. Here, novel sensory information is integrated on very short time-scales to cancel an already planned action. The frontal cortex is believed to play a crucial role in the temporal organization of goal-directed behavior and cognitive control and is implicated in stopping a motor response. Using the high spatiotemporal resolution of electrocorticography (ECoG), we found evidence for two distinct processes localized to the middle frontal gyrus (MFG). High-frequency band (HFB) power increased in stop-trials before the stop-signal reaction time (SSRT), showing no difference between successful and unsuccessful stops. We interpret this activation as contributing to the stopping process, either by signaling the stop-signal itself, or by implementing attentional control. A second HFB activation was observed after the go and stop processes have finished, and was larger for unsuccessful stops, and is likely related to behavioral monitoring. Our results support the notion that frontal cortex implements different functions related to stopping. Implementing the perception-action cycle not only involves re-acting to novel information from the senses in a bottom-up manner. It is believed that the brain also implements a strategy anticipating future events based on prior knowledge. Here we investigated how anticipation of sounds influences auditory processing. Using both EEG and ECoG, we employed a task with omissions of expected sounds, thereby isolating endogenous responses to expectations in auditory cortex. We found that a subset of auditory active electrodes in lateral superior temporal gyrus (STG) and superior temporal sulcus (STS) showing HFB power increases to omissions. We were able to successfully decode whether the subject heard the syllable ‘Ba’ or ‘Ga’. However, which sound was omitted could not be decoded from auditory active sites, nor from the omission HFB increase specifically. We also observed a negative ERP in posterior STG in the intracranial data, which may be related to an auditory cortical generator of the N2 component. In a separate EEG studies we also observed both an N2 negativity, as well as a negativity occurring before the intracranial negativity, the source of which may be in A1, a region which we could not access intracranially. Finally, a P3a ERP was observed in EEG, which points to both the HFB and ERP effects in posterior STG to be signatures of auditory-specific salience or mismatch detection.