Maturation of the P3 and concurrent oscillatory processes during adolescence.

OBJECTIVE: During adolescence event-related modulations of the neural response may increase. For slow event-related components, such as the P3, this developmental change may be masked due to increased amplitude levels of ongoing delta and theta oscillations in adolescents. METHODS: In a cross-sectional study design, EEG was measured in 51 participants between 13 and 24years. A visual oddball paradigm was used to elicit the P3. Our analysis focused on fronto-parietal activations within the P3 time-window and the concurrent time-frequency characteristics in the delta (∼0.5-4Hz) and theta (∼4-7Hz) band. RESULTS: The parietal P3 amplitude was similar across the investigated age range, while the amplitude at frontal regions increased with age. The pre-stimulus amplitudes of delta and theta oscillations declined with age, while post-stimulus amplitude enhancement and inter-trial phase coherence increased. These changes affected fronto-parietal electrode sites. CONCLUSIONS: The parietal P3 maximum seemed comparable for adolescents and young adults. Detailed analysis revealed that within the P3 time-window brain maturation during adolescence may lead to reduced spontaneous slow-wave oscillations, increased amplitude modulation and time precision of event-related oscillations, and altered P3 scalp topography. SIGNIFICANCE: Time-frequency analyses may help to distinguish selective neurodevelopmental changes within the P3 time window.

Altered alpha brain oscillations during multistable perception in schizophrenia.

Schizophrenia is a complex mental disorder with impairments in integrating sensory and cognitive functions, leading to severe problems in coherent perception. This impairment might be accelerated during multistable perception. Multistable perception is a phenomenon, where a visual pattern gives rise to at least two different perceptual representations. We addressed this issue by assessing event-related alpha oscillations during continuous viewing of an ambiguous and unambiguous control stimulus. Perceptual reversals were indicated by a manual response, allowing differentiation between phases of reversion and non-reversion (that is perceptual stability) in both tasks. During the ambiguous task, patients and controls showed a comparable number of perceptual reversals. Alpha amplitudes in patients were larger in non-reversion phases, accompanied by a stronger decrease of alpha activity preceding the perceptual reversal. This group difference was pronounced for lower alpha activity and not apparent during the unambiguous task. This indicates that ambiguous perception taps into the specific deficits that patients experience in maintaining coherent perception. Given that top-down influences in generating a meaningful percept seems to be low in patients, they appear more dependent on sensory information. Similar, bottom-up mechanisms might be more important in triggering perceptual reversals in patients than in controls.

Frontal theta activity is pronounced during illusory perception.

Object perception is driven by sensory information as well as expectations and prior experiences. The latter influence may increase when the sensory information is poor or inconclusive. Visual illusions, for example induced by ambiguous stimuli, provide a tool to investigate perceptual uncertainty, because ambiguous stimuli elicit switching between at least two perceptual alternatives. Theta oscillations may reflect the impact of visual illusion on perception since they are specifically important to coordinate information in large-scale brain networks, including visual sensory as well as higher-order brain areas. Theta responses elicited by an ambiguous and an unambiguous apparent motion-inducing stimulus were compared, thereby differentiating time periods of perceptual switching and perceptual stability (non-switching). The theta responses were larger at anterior than at posterior sites. This gradient was stronger during the ambiguous task than during the unambiguous task, even though sensory stimulation was comparable for both tasks. A transient increase of the theta response occurred during switching time periods for both the ambiguous and the unambiguous tasks, indicating that the theta response related to the perceptual switch might not be affected by the ambiguity of the stimulus. Irrespective of the percept switching or not, ambiguous stimuli elicited an enduring more prominent activation of higher-order rather than visual sensory brain areas. This indicates an increased reliance on expectations and prior information to ensure coherent object perception in particular when the visual information is degraded or elicits an ongoing conflict between perceptual interpretations.