State Regulation and Executive Function in Traumatic Brain Injury: EEG Correlates of Impairment and Intervention

Executive dysfunction is a common and persistent consequence of Traumatic Brain Injury (TBI) and has a significant detrimental impact on social, emotional, and occupational functioning. Abnormalities in EEG measures reflecting the energetic state of the brain are also common following TBI, and rehabilitation approaches such as cognitive and neurofeedback training aim to improve executive function (EF) by facilitating changes in brain state and function. However, the field is lacking a parsimonious and clinically applicable theory of the relationship between brain energetic state and cognition in TBI. The Cognitive Energetic Model (CEM; Sanders, 1983) may address this gap. The CEM provides an explanation of how two aspects of energetic state - arousal (baseline energetic state) and activation (mobilisation of arousal in response to processing demands) - interact with computational factors, effort, and evaluative processes to produce efficient cognitive performance. EEG measures of arousal (eyes-closed global alpha) and activation (changes in delta, theta, alpha, and beta bands between resting or task conditions) provide an empirical basis for investigating the applicability of this model to TBI sequelae and intervention. The aims of this thesis were: 1) to investigate the applicability of the CEM arousal and activation concepts to understanding energetic state abnormalities and their relationship to EF impairment in TBI; and 2) to investigate the effectiveness of a CEM-based neurocognitive training program for improving EF in TBI. Study 1 investigated EEG measures of arousal and activation recorded during eyes-closed and eyes-open resting conditions. Results showed intact arousal, but impaired activation for the TBI group, compared to healthy controls. The TBI group were characterised by reduced resting theta activation and a trend toward increased resting delta activation. Furthermore, enhanced resting delta and alpha activation and reduced resting theta activation were associated with impaired performance on a response inhibition task across groups. Together, the results suggested that it is not baseline resting state, but rather the ability to mobilise energetic state, that is impaired in TBI, and that this is associated with impaired EF