Brain maturation during adolescence and young adulthood - an EEG study

Objective: Adolescence is a period of major maturational changes in the brain. It is particularly the maturation of the frontal cortex and its interactions with other brain regions that dominates this late stage of development and has important implications for the cognitive abilities during the entire adult life. Methods: In this thesis, developmental changes in the delta (0 - 4 Hz), theta (4 - 7 Hz) and gamma (28 - 48 Hz) frequency bands were investigated in adolescents (13 - 15 years) and adults (20 - 27 years) during resting and cognitive states. Four tasks were conducted: the spontaneous EEG (eyes-open), the ambiguous task, the unambiguous task and the visual oddball task. During the ambiguous task, participants were exposed to the Stroboscopic Ambiguous Motion (SAM) paradigm. SAM is a multistable stimulus that, when viewed continuously, induces internally-generated changes in the perceived direction of motion. For the unambiguous task, a modified version of the SAM was used. In this case, the perceived direction of motion was controlled externally. In the visual oddball task, randomly interspersed targets had to be identified in a train of frequent non-targets. Single-trial amplitudes of delta, theta and gamma activity obtained during the spontaneous EEG were compared between the groups to assess general maturational changes in the developing brain. The task-related enhancement of the oscillatory activity was compared between the groups in order to assess developmental changes in task performance. Results: The previous findings of delta and theta amplitudes decreasing with age during the spontaneous EEG were replicated. Similarly to previous studies, our results also indicate that for spontaneous EEG gamma amplitudes do not profoundly differ between adolescents and adults. Moreover, the present study supports previous findings from adult research which have established a functional relationship between delta, theta and gamma activities and higher cognitive processes. It has further been found that the developmental changes correlated with task difficulty. Only for the - most challenging - ambiguous task the gamma oscillations were found to reflect a change in task-related cortical processing during adolescence, whereas no age-related differences of gamma responses were detected for less demanding tasks (the unambiguous and visual oddball tasks). The event-related theta responses were found to increase with age for the ambiguous and visual oddball tasks and did not depend on age for the unambiguous task. Furthermore, the event-related delta responses increased with age for all tasks. Conclusions: The main finding of this study is that functional networks of delta, theta and gamma activity undergo maturational changes during adolescence. The found differences in the task-related activations may indicate a protracted development of higher-order cognitive processes during adolescence. The developmental changes of task-related activations seem to vary with task difficulty and frequency band. Significance: Systematic studies on developmental changes of brain oscillations in cognitive tasks are still infrequent and specifically the time period of adolescence has been rarely investigated. The typical age of onset for mental disorders, such as schizophrenia, is the late stages or shortly after the onset of adolescence, rendering the outcome of brain maturation during this period of immense importance for life-long mental health. Thus, it is critical to extend our understanding of the mechanism behind the appearance of cognitive functions during adolescence

Entwicklung des Gehirns in der Adoleszenz und im jungen Erwachsenalter - eine EEG-Studie

Objective: Adolescence is a period of major maturational changes in the brain. It is particularly the maturation of the frontal cortex and its interactions with other brain regions that dominates this late stage of development and has important implications for the cognitive abilities during the entire adult life. Methods: In this thesis, developmental changes in the delta (0 - 4 Hz), theta (4 - 7 Hz) and gamma (28 - 48 Hz) frequency bands were investigated in adolescents (13 - 15 years) and adults (20 - 27 years) during resting and cognitive states. Four tasks were conducted: the spontaneous EEG (eyes-open), the ambiguous task, the unambiguous task and the visual oddball task. During the ambiguous task, participants were exposed to the Stroboscopic Ambiguous Motion (SAM) paradigm. SAM is a multistable stimulus that, when viewed continuously, induces internally-generated changes in the perceived direction of motion. For the unambiguous task, a modified version of the SAM was used. In this case, the perceived direction of motion was controlled externally. In the visual oddball task, randomly interspersed targets had to be identified in a train of frequent non-targets. Single-trial amplitudes of delta, theta and gamma activity obtained during the spontaneous EEG were compared between the groups to assess general maturational changes in the developing brain. The task-related enhancement of the oscillatory activity was compared between the groups in order to assess developmental changes in task performance. Results: The previous findings of delta and theta amplitudes decreasing with age during the spontaneous EEG were replicated. Similarly to previous studies, our results also indicate that for spontaneous EEG gamma amplitudes do not profoundly differ between adolescents and adults. Moreover, the present study supports previous findings from adult research which have established a functional relationship between delta, theta and gamma activities and higher cognitive processes. It has further been found that the developmental changes correlated with task difficulty. Only for the - most challenging - ambiguous task the gamma oscillations were found to reflect a change in task-related cortical processing during adolescence, whereas no age-related differences of gamma responses were detected for less demanding tasks (the unambiguous and visual oddball tasks). The event-related theta responses were found to increase with age for the ambiguous and visual oddball tasks and did not depend on age for the unambiguous task. Furthermore, the event-related delta responses increased with age for all tasks. Conclusions: The main finding of this study is that functional networks of delta, theta and gamma activity undergo maturational changes during adolescence. The found differences in the task-related activations may indicate a protracted development of higher-order cognitive processes during adolescence. The developmental changes of task-related activations seem to vary with task difficulty and frequency band. Significance: Systematic studies on developmental changes of brain oscillations in cognitive tasks are still infrequent and specifically the time period of adolescence has been rarely investigated. The typical age of onset for mental disorders, such as schizophrenia, is the late stages or shortly after the onset of adolescence, rendering the outcome of brain maturation during this period of immense importance for life-long mental health. Thus, it is critical to extend our understanding of the mechanism behind the appearance of cognitive functions during adolescence