Neural Mechanisms of Erp Change: Combining Insights From Electrophysiology and Mathematical Modeling

Abstract

Using a standardized database of EEG data, recorded during the habituation and oddball paradigms, changes in the auditory event-related potential (ERP) are demonstrated on the time scale of seconds and minutes. Based on previous research and a mathematical model of neural activity, neural mechanisms that could account for these changes are proposed. When the stimulus tones are not relevant to a task, N100 magnitude decreases substantially for the first repetition of a stimulus pattern and increases in response to a variant tone. It is argued these short-term changes are consistent with the hypothesis that there is a refractory period in the neural elements underlying the ERP. In the oddball paradigm, when the stimulus tones are task-relevant, the magnitudes of both N100 and P200 for backgrounds decrease over the entire six-minute recording session. It is argued that these changes are mediated by a decreasing arousal level, and consistent with this, a subject's electrodermal activity (EDA) is shown to reduce over the recording session. By fitting ERPs generated by a biophysical model of neural activity, it is shown that the changes in the background ERPs over the recording session can be reproduced by changing the strength of connections between populations of cortical neurons. For ERPs elicited by infrequent stimuli, there is no corresponding trend in the magnitudes of N100 or P300 components. The effects of stimuli serial order on ERPs are also assessed, showing that the N100 for background ERPs and the N100 and P300 for target ERPs increases as the probability, and expectancy, of receiving a task relevant stimulus increases. Cortical neuromodulation by acetylcholine (ACh) is proposed as a candidate mechanism to mediate the ERP changes associated with attention and arousal.

Distributed processing; distributed functions?

“…Most recent developments in modeling have focused on electromagnetic (EEG and MEG) data (David et al, 2006; Kiebel et al, 2006, 2007; Garrido et al, 2007a,b; Clearwater et al, 2008; Chen et al, 2008; Garrido et al, 2008), with related developments to cover local field potential (LFP) recordings (Moran et al, 2007, 2008). These models are more sophisticated than the neuronal models for fMRI and are based upon neural-mass or mean-field models of interacting neuronal populations (see Deco et al, 2008).…”

Reduced habituation of auditory evoked potentials indicate cortical hyper-excitability in Fragile X Syndrome

“…Adding this probe of expectancy effects adds cognitive complexity and variable attentional influences to the assessment of basic auditory processing. 12 , 16 , 19 , 20 , 21 Second, stimuli in prior studies were separated by relatively long inter-stimulus intervals, which can diminish habituation effects, as refractory circuits significantly complete their recovery after intervals longer than 500 ms. 22 , 23 When tones are presented in sequence with a shortened inter-stimulus interval and without novel distracters, cognitive factors are limited and habituation effects seen in N1 reduction to repeated tones are increased. Limiting cognitive factors is particularly important when assessing sensory processing in groups with cognitive deficits such as FXS, where group differences in cognitive processing could obscure results.…”

N100, N200, and P300 Auditory Event-Related Potentials Depending on Handedness and Response Tasks such as Button Pressing and Mental Counting

“…Smaller N100 and larger P300 amplitudes for the button pressing task and shorter N200 latency and larger P300 amplitude of left-handed participants were found. The N100 amplitude was relatively large as it was the first stimulus in a series, but it became smaller due to subsequent stimulus repetitions (Clearwater et al, 2008;Michalski, 2000). However, this sequen-smaller N200 amplitude in the button pressing task for both right-and left-handed participants, larger P300 amplitude in women for both right-and left-handed, shorter N100 latency when using the left thumb of the button pressing task for both right-and left-handed, and shorter N100 latency and larger N100 and P300 amplitudes in both right-and left-handed women when using both right and left thumbs for the button pressing task (Tables 2 and 3).…”

“…The N100 response was modulated by the physical characteristics of stimuli such as type, intensity, and duration, and also depended on subject factors such as the internal state, neural activity, and cognition. As it was the first stimulus in a series, the N100 amplitude was relatively high but lowered for subsequent repetitions of stimuli (Brown et al, 2002;Clearwater et al, 2008). N200 has been known to be a comprehensive response of cortical, thalamic, and brainstem regions, although the source of N200 activation relied on some extent to the limbic and complex generating system in the region of the thalamus (Ponton et al, 2002).…”