Oscillatory brain electrical potentials in developmental psychopathology and form perception

Brain imaging studies of developmental disorders involving cognitive impairment have typically emphasized stimulus evoked neural activity. An implicit assumption is that the application of experimental paradigms employed in cognitive neuroscience should inform cognitive and anatomical conceptualizations of the disorders in question. In studies of developmental psychopathology, this conceptual framework has not accounted for the contributions of stable, ongoing, stationary brain processes that may influence stimulus evoked responses. This is a particularly important issue when considering data from patient populations, who may express fundamental differences in brain architecture or neuromodulatory systems. Ignoring this relationship could lead to confusing generalized physiological pathology with specific cognitive processes probed in experimental paradigms.;In chapters 1 of the dissertation, the spontaneous electroencephalogram (EEG) from 65 pediatric subjects is considered. 44 of these subjects were diagnosed with Attention Deficit/Hyperactivity Disorder (ADHD), a pervasive pediatric disorder. A long record of spontaneous EEG, generated by subjects in an eyes closed resting state, is examined using spectral power and coherence methods. Robust differences between groups are seen in paired sensor coherence, a measure of functional brain connectivity. ADHD subjects reliably express more coherent oscillations in the low alpha and mid beta EEG bands than controls. Conversely, at most naturally occurring peak frequencies in the EEG power spectrum, ADHD subjects reliably produce less power and coherence than Controls.;Chapter 2 examines the EEG in an eyes open, alert state during a cognitive task. Group coherence and power differences, comparable to the spontaneous EEG, are found in the pre- and post-stimulus EEG. Stimulus related brain activity is characterized by analysis of phase-locked evoked potentials and non-phase locked induced potentials. Evoked responses, especially in the low theta band, are found to be substantially reduced in ADHD. The dominant frequency component of the evoked potential is shown to be independent of ongoing brain activity in the pre-stimulus period.;Chapter 3 considers neural correlates of visual form perception in normal adult subjects. Psychophysical signal detection methods are used in conjunction with EEG recording. The Hilbert transform is employed as a joint time/frequency measure of brain activity associated with perception of Glass patterns.