M.Sc Thesis

M.Sc StudentNahmany Goldberg Nadia
SubjectCerebral electrical activity during content and spatially
cued attention task in adult ADHD subjects
DepartmentDepartment of Medicine
Supervisor PROFESSOR EMERITUS Hillel Pratt
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Attention Deficit and Hyperactivity Disorder (ADHD) is a neuro-developmental syndrome characterized by inattention, impaired inhibition and increased motor activity. One of the core deficiencies in ADHD manifests in aberrant executive functions. A new content and spatially cued auditory attention paradigm was developed in our laboratory. The paradigm consists of 3-dimensioned auditory stimuli given to the subject binaurally, and switching instructions that are given to the subject throughout the task, allowing the same physical stimulus to receive different contexts and to be processed differently. We examined the paradigm in 13 adult ADHD subjects and compared the behavioral and the electrophysiological measures to 15 normally-developed adults. Performance was estimated by means of accuracy and reaction times in each group. Brain electrical activity was recorded from 61 electrodes attached to the scalp and ERPs were extracted from the continuous electroencephalographic records . The behavioral results showed that ADHD subjects were less accurate and had longer reaction times than controls. The ERP analysis revealed significant differences between groups both in early and late components. In the ADHD group, N2 latency was significantly longer and P3 amplitude was significantly smaller in all experimental conditions. In addition, in some of the experimental conditions the ADHD subjects showed a shorter N1 latency, a smaller N2 amplitude, longer N2 and P3 latencies, and a smaller LPC mean amplitude. A Support Vector Machine algorithm was employed to test the mean classification accuracy of the study paradigm, and showed an accuracy of 88%. The behavioral results replicated earlier findings showing that ADHD involves impaired performance in attentional tasks. The electrophysiological findings showed that the differences between groups begun at the early stages of information processing. ADHD subjects had difficulties in the initial extraction of information regarding the physical characteristics of incongruent stimuli in the Stroop effect and faster processing of stimulus features as reflected by N1. The changes in P2 parameters suggested impaired control of the inhibition processes. In addition to the early stages disparity, differences were found at the advanced stages of cognitive processing as reflected in the late components N2, P3 and LPC. ADHD subjects showed increased cognitive efforts during the task-related cognitive processing, together with inadequate and ineffective resources allocation. The stimulus identification and evaluation processes were longer and more attentional resources were allocated. The findings support the theory of impaired executive control in ADHD subjects alongside an inadequate alerting network. Moreover, changes were found in voice gender recognition processes and ear advantage mechanisms . The results suggest that the differences between ADHD subjects and normal population begin at the early stages of information processing and continue through the advanced levels of cognitive processing. In addition, we showed that the novel study paradigm combines the characteristics of several known neuro-psychological tasks such as Cued Attention and Stroop, and can differentiate between ADHD and control subjects by means of behavioral and electrophysiological measurements.