Exploring Electrophysiological Correlates of Cognitive Functions: A Visual Evoked Potential Study
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Introduction: While the functional neuroanatomy of cognition at a structural level has been well studied, understanding the underlying neural mechanisms that support specific cognitive abilities is a relatively new field of research. The current study utilizes a battery of neurophysiological tests that were designed to examine specific neural mechanisms involved in early-stage visual processing to investigate electrophysiological correlates of cognitive functions, as measured by well-established neuropsychological tests. Methods: Participants included 37 healthy individuals ( Mage, = 21.08 yrs, SD = 5.01; Meducation = 13.38 yrs, SD = 1.69). Gender was split nearly equally, with a small majority of the population being female (n = 19, 51.4°/x). Using a Neucodia system (VeriSci Corp.), steady-state and transient visual evoked potentials (VEPs) were elicited by stimuli according to a protocol of tests, including the following conditions: appearance-disappearance of bright-and dark-isolated checks with swept contrast, contrast-reversing checkerboards, sinusoidal modulation of radial patterns, and a grating pattern swept in spatial frequency. VEP measures analyzed included amplitude, phase, latency, neural noise, signal-to-noise ratios, and coherence estimates of frequency mechanisms. In addition, all participants were also administered a battery of well-established neuropsychological tests to measure various cognitive domains, including the Benton Judgement of Line Orientation Test, the Brief Visuospatial Memory Test-Revised, The Sorting Test of the Delis-Kaplan Executive Function System, the Symbol Digit Modalities Test, Trail Making Test – Trial A and B, and the Wechsler Test of Adult Reading. Correlations between electrophysiological measures and cognitive performance on the neuropsychological tests were examined, and multiple regression analyses were performed. Furthermore, the moderating effect of gender on these relationships was explored. Results: Negative associations were found between latency of an early negative deflection (N75) in the transient VEP (tVEP) and performance on a task of speeded cognitive flexibility (TMT-B) (rs: -.35 – -.47, ps < .05). Measures of neural noise in VEP responses to grating and radial patterns were negatively correlated with performance on tasks of visual learning, executive functioning, and estimated intellectual functioning (rs: -.33 – -.44, ps < .05). However, variability in response (neural noise) to bright- and dark-isolated checks was positively correlated with performance on a task of executive functioning, which contradicted the hypothesis (rs: .33 – .46, ps < .05). Signal-to-noise ratios in VEP responses to bright-isolated checks, radial, and grating patterns were positively associated with performance on measures of processing speed, visuoperceptual judgment, and estimated intellectual functioning (rs: .33 – .47, ps < .05). All hypothesized relationships were moderated by gender (ps : .001 – .072). Discussion: Overall, while this study had limitations such as a relatively small sample size including participants with similar educational attainment, results show promise for the use of VEP measures as a way to quantify and understand cognitive functions.