Oscillatory Control over Representational States in Working Memory

In the visual world, attention is guided by perceptual goals activated in visual working memory (VWM). However, planning multiple-task sequences also requires VWM to store representations for future goals. These future goals need to be prevented from interfering with the current perceptual task. Recent findings have implicated neural oscillations as a control mechanism serving the implementation and switching of different states of prioritization of VWM representations. We review recent evidence that posterior alpha-band oscillations underlie the flexible activation and deactivation of VWM representations and that frontal delta-to-theta-band oscillations play a role in the executive control of this process. That is, frontal delta-to-theta appears to orchestrate posterior alpha through long-range oscillatory networks to flexibly set up and change VWM states during multitask sequences

Oscillatory Mechanisms of Preparing for Visual Distraction

Evidence shows that observers preactivate a target representation in preparation of a visual selection task. In this study, we addressed the question if and how preparing to ignore an anticipated distractor differs from preparing for an anticipated target. We measured EEG while participants memorized a laterally presented color, which was cued to be either a target or a distractor in two subsequent visual search tasks. Decoding the location of items in the search display from EOG channels revealed that, initially, the anticipated distractor attracted attention and could only be ignored later during the trial. This suggests that distractors could not be suppressed in advance but were represented in an active, attention-guiding format. Consistent with this, lateralized posterior alpha power did not dissociate between target and distractor templates during the delay periods, suggesting similar encoding and maintenance. However, distractor preparation did lead to relatively enhanced nonlateralized posterior alpha power, which appeared to gate sensory processing at search display onset to prevent attentional capture in general. Finally, anticipating distractors also led to enhanced midfrontal theta power during the delay period, a signal that was predictive of how strongly both target and distractor were represented in the search display. Together, our results speak against a distractor-specific advance inhibitory template, thus contrary to the preactivation of specific target templates. Rather, we demonstrate a general selection suppression mechanism, which serves to prevent initial involuntary capture by anticipated distracting input

Brain oscillations and novelty processing in human spatial memory

Hippocampal activity in rodent model systems is commonly associated with movement and exploratory behaviour, while human hippocampal research has traditionally focused on mnemonic function. I attempted to bridge this gap with a set of experiments where human participants performed an interactive virtual navigation paradigm that resembled rodent spatial exploration tasks, in conjunction with neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). I then used this interactive paradigm to examine the oscillatory correlates of memory, novelty and the behavioural relevance of the default mode network. The first experiment used MEG and fMRI to examine whether the movement-related theta rhythm (4-8 Hz) recorded from the rodent hippocampus has a measurable human analog. I found that the human hippocampal theta rhythm supports memory, and may coordinate exploratory movements in the service of self-directed learning. In further analyses in Experiment 2, during cued spatial memory retrieval, I observed that medial prefrontal cortex theta phase couples with ongoing theta oscillations in the right anterior medial temporal lobe and with neocortical gamma (65-85 Hz) amplitude. In Experiment 3, with fMRI I investigated the effect of environmental novelty versus object novelty during the navigation task and found that hippocampal activity is modulated only by environmental novelty, while the fusiform gyrus/posterior parahippocampal cortex responded to object novelty. Finally, in Experiment 4 using 3T and high-field 7T fMRI, I investigated endogenous (task-free) periods that flanked different stages of a spatial navigation paradigm to determine how endogenous slow oscillations in the default mode network correlate with subsequent spatial memory performance and found mixed evidence that default mode network activity predicts individual performance. Finally, I discuss my results in the context of recent findings in spatial memory and novelty processing, and consider the relationship between the human hippocampus and rodent model systems

Long-range alpha and beta and short-range gamma EEG synchronization distinguishes phasic and tonic REM periods

info:eu-repo/semantics/publishe

Altered event-related potentials and theta oscillations index auditory working memory deficits in healthy aging

Speech comprehension deficits constitute a major issue for an increasingly aged population, as they may lead older individuals to social isolation. Since conversation requires constant monitoring, updating and selecting information, auditory working memory decline, rather than impoverished hearing acuity, has been suggested a core factor. However, in stark contrast to the visual domain, the neurophysiological mechanisms underlying auditory working memory deficits in healthy aging remain poorly understood, especially those related to on-the-fly information processing under increasing load. Therefore, we investigated the behavioral costs and electrophysiological differences associated with healthy aging and working memory load during continuous auditory processing. We recorded EEG activity from 27 younger (∼25 years) and 29 older (∼70 years) participants during their performance on an auditory version of the n-back task with speech syllables and 2 workload levels (1-back; 2-back). Behavioral measures were analyzed as indices of function; event-related potentials as proxies for sensory and cognitive processes; and theta oscillatory power as a reflection of memory and central executive function. Our results show age-related differences in auditory information processing within a latency range that is consistent with a series of impaired functions, from sensory gating to cognitive resource allocation during constant information updating, especially under high load