TY - JOUR T1 - Modulation in cortical excitability disrupts information transfer in perceptual-level stimulus processing. JF - Neuroimage Y1 - 2021 A1 - Moheimanian, Ladan A1 - Paraskevopoulou, Sivylla E A1 - Adamek, Markus A1 - Schalk, Gerwin A1 - Peter Brunner KW - Acoustic Stimulation KW - Adult KW - Aged KW - Alpha Rhythm KW - Auditory Cortex KW - Brain Mapping KW - Cortical Excitability KW - Electrocorticography KW - Female KW - Humans KW - Male KW - Middle Aged AB -

Despite significant interest in the neural underpinnings of behavioral variability, little light has been shed on the cortical mechanism underlying the failure to respond to perceptual-level stimuli. We hypothesized that cortical activity resulting from perceptual-level stimuli is sensitive to the moment-to-moment fluctuations in cortical excitability, and thus may not suffice to produce a behavioral response. We tested this hypothesis using electrocorticographic recordings to follow the propagation of cortical activity in six human subjects that responded to perceptual-level auditory stimuli. Here we show that for presentations that did not result in a behavioral response, the likelihood of cortical activity decreased from auditory cortex to motor cortex, and was related to reduced local cortical excitability. Cortical excitability was quantified using instantaneous voltage during a short window prior to cortical activity onset. Therefore, when humans are presented with an auditory stimulus close to perceptual-level threshold, moment-by-moment fluctuations in cortical excitability determine whether cortical responses to sensory stimulation successfully connect auditory input to a resultant behavioral response.

VL - 243 ER - TY - JOUR T1 - Within-subject reaction time variability: Role of cortical networks and underlying neurophysiological mechanisms. JF - Neuroimage Y1 - 2021 A1 - Paraskevopoulou, Sivylla E A1 - Coon, William G A1 - Peter Brunner A1 - Miller, Kai J A1 - Schalk, Gerwin KW - Adult KW - Algorithms KW - Alpha Rhythm KW - Cerebral Cortex KW - Connectome KW - Electrocorticography KW - Female KW - Gamma Rhythm KW - Humans KW - Male KW - Middle Aged KW - Nerve Net KW - Psychomotor Performance KW - Reaction Time KW - Young Adult AB -

Variations in reaction time are a ubiquitous characteristic of human behavior. Extensively documented, they have been successfully modeled using parameters of the subject or the task, but the neural basis of behavioral reaction time that varies within the same subject and the same task has been minimally studied. In this paper, we investigate behavioral reaction time variance using 28 datasets of direct cortical recordings in humans who engaged in four different types of simple sensory-motor reaction time tasks. Using a previously described technique that can identify the onset of population-level cortical activity and a novel functional connectivity algorithm described herein, we show that the cumulative latency difference of population-level neural activity across the task-related cortical network can explain up to 41% of the trial-by-trial variance in reaction time. Furthermore, we show that reaction time variance may primarily be due to the latencies in specific brain regions and demonstrate that behavioral latency variance is accumulated across the whole task-related cortical network. Our results suggest that population-level neural activity monotonically increases prior to movement execution, and that trial-by-trial changes in that increase are, in part, accounted for by inhibitory activity indexed by low-frequency oscillations. This pre-movement neural activity explains 19% of the measured variance in neural latencies in our data. Thus, our study provides a mechanistic explanation for a sizable fraction of behavioral reaction time when the subject's task is the same from trial to trial.

VL - 237 ER -