Cortical networks dynamically emerge with the interplay of slow and fast oscillations for memory of a natural scene

Top-down and bottom-up attention cause the ventriloquism effect with distinct electroencephalography modulations

The ventriloquism effect is a critical phenomenon for understanding the underlying mechanisms of multisensory integration. Cross-modal spatial attention causes a distortion of sound localization, although the neural basis of the effect remains an unanswered question. We hypothesized that top-down and bottom-up visual-spatial attention causes the ventriloquism effect with different modulations of ongoing neural oscillation. To test this hypothesis, human scalp electroencephalography (EEG) was measured during a sound localization task. Top-down attention suppressed the EEG amplitude in the alpha frequency (10 Hz) over the contralateral temporal electrode sites to visual cue hemifields. Bottom-up attention shifted the EEG phase to the theta frequency (7 Hz), rather than suppressing the amplitude. Two different neural mechanisms of ongoing neural oscillation contributed toward the ventriloquism effect, with different spatial attention.

Ongoing slow oscillatory phase modulates speech intelligibility in cooperation with motor cortical activity

Neural oscillation is attracting attention as an underlying mechanism for speech recognition. Speech intelligibility is enhanced by the synchronization of speech rhythms and slow neural oscillation, which is typically observed as human scalp electroencephalography (EEG). In addition to the effect of neural oscillation, it has been proposed that speech recognition is enhanced by the identification of a speaker’s motor signals, which are used for speech production. To verify the relationship between the effect of neural oscillation and motor cortical activity, we measured scalp EEG, and simultaneous EEG and functional magnetic resonance imaging (fMRI) during a speech recognition task in which participants were required to recognize spoken words embedded in noise sound. We proposed an index to quantitatively evaluate the EEG phase effect on behavioral performance. The results showed that the delta and theta EEG phase before speech inputs modulated the participant’s response time when conducting speech recognition tasks. The simultaneous EEG-fMRI experiment showed that slow EEG activity was correlated with motor cortical activity. These results suggested that the effect of the slow oscillatory phase was associated with the activity of the motor cortex during speech recognition.

The impact of experienced stress on aged spatial discrimination: Cortical overreliance as a result of hippocampal impairment

A large body of neuroscientific work indicates that exposure to experienced stress causes damage to both cortical and hippocampal cells and results in impairments to cognitive abilities associated with these structures. Similarly, work within the domain of cognitive aging demonstrates that elderly participants who report experiencing greater amounts of stress show reduced levels of cognitive functioning. The present article attempted to combine both findings by collecting data from elderly and young participants who completed a spatial discrimination paradigm developed by Reagh and colleagues [Reagh et al. (2013) Hippocampus 24:303-314] to measure hippocampal-mediated cognitive processes. In order to investigate the effect of stress on the cortex and, indirectly, the hippocampus, it paired the paradigm with electroencephalographic recordings of the theta frequency band, which is thought to reflect cortical/hippocampal interactions. Findings revealed that elderly participants with high levels of experienced stress performed significantly worse on target recognition and lure discrimination and demonstrated heightened levels of cortical theta synchronization compared with young and elderly low stress counterparts. Results therefore provided further evidence for the adverse effect of stress on cognitive aging and indicate that impaired behavioral performance among high stress elderly may coincide with an overreliance on cortical cognitive processing strategies as a result of early damage to the hippocampus.