Localization of Cortical Phase and Amplitude Dynamics during Visual Working Memory Encoding and Retention

Neuroscience Center, University of Helsinki, 00014 Helsinki, Finland.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 03/2011; 31(13):5013-25. DOI: 10.1523/JNEUROSCI.5592-10.2011
Source: PubMed


Several studies show that the amplitudes of human brain oscillations are modulated during the performance of visual working memory (VWM) tasks in a load-dependent manner. Less is known about the dynamics and identities of the cortical regions in which these modulations take place, and hence their functional significance has remained unclear. We used magnetoencephalography and electroencephalography together with minimum norm estimate-based source modeling to study the dynamics of ongoing brain activity during a parametric VWM task. Early stimulus processing and memory encoding were associated with a memory load-dependent spread of neuronal activity from occipital to temporal, parietal, and frontal cortical regions. During the VWM retention period, the amplitudes of oscillations in theta/alpha- (5-9 Hz), high-alpha- (10-14 Hz), beta- (15-30 Hz), gamma- (30-50 Hz), and high-gamma- (50-150 Hz) frequency bands were suppressed below baseline levels, and yet, in frontoparietal regions, load dependently strengthened. However, in occipital and occipitotemporal structures, only beta, gamma, and high-gamma amplitudes were robustly strengthened by memory load. Individual behavioral VWM capacity was predicted by both the magnitude of the N1 evoked response component in early visual regions and by the amplitudes of frontoparietal high-alpha and high-gamma band oscillations. Thus, both early stimulus processing and late retention period activities may influence the behavioral outcome in VWM tasks. These data support the notion that beta- and gamma-band oscillations support the maintenance of object representations in VWM whereas alpha-, beta-, and gamma-band oscillations together contribute to attentional and executive processing.

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Available from: Satu Palva, Oct 06, 2015
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    • "These results are in agreement with the relationships previously identified between central executive, working memory processes and fronto-parietal electrode coupling [31]. Moreover, the general functional scheme used here matches that applied in a previous study where similar relationships between central executive and working memory processes, and fronto-parietal electrode coupling were described [32]. Regarding the specific location of the changes in EEG signal, our results confirm that Stroop interference involves the right frontal cortex (lateral and basal prefrontal areas –Fp2-), and posterior fronto-sagittal ones, Fz, as proposed from previous fMRI clinical studies in healthy controls and patients with schizophrenia [33]. "
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    ABSTRACT: The Stroop effect is considered as a standard attentional measure to study conflict resolution in humans. The response of the brain to conflict is supposed to change over time and it is impaired in certain pathological conditions. Neuropsychological Stroop test measures have been complemented with electroencephalography (EEG) techniques to evaluate the mechanisms in the brain that underlie conflict resolution from the age of 20 to 70. To study the changes in EEG activity during life, we recruited a large sample of healthy subjects of different ages that included 90 healthy individuals, divided by age into decade intervals, which performed the Stroop test while recording a 14 channel EEG. The results highlighted an interaction between age and stimulus that was focused on the prefrontal (Alpha and Theta band) and Occipital (Alpha band) areas. We concluded that behavioural Stroop interference is directly influenced by opposing Alpha and Theta activity and evolves across the decades of life.
    PLoS ONE 05/2014; 9(5):e95657. DOI:10.1371/journal.pone.0095657 · 3.23 Impact Factor
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    • "In addition, several studies have shown that frontal theta increases are correlated with memory load, in that larger memory loads (e.g., 5 items compared 3 items) are associated with stronger frontal theta activity [40]–[41], [43]–[44]. There is also some evidence that frontal alpha activity increases with memory load [42], although these reports have been less frequent. More commonly, alpha activity has been linked to active inhibition of task irrelevant brain regions during attention and working memory tasks [45]–[46], with some data further suggesting that alpha-frequency activity may be a critical mechanism for overall network coordination during cognitive processing [42], [46]. "
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    ABSTRACT: Shortly after infection, HIV enters the brain and causes widespread inflammation and neuronal damage, which ultimately leads to neuropsychological impairments. Despite a large body of neuroscience and imaging studies, the pathophysiology of these HIV-associated neurocognitive disorders (HAND) remains unresolved. Previous neuroimaging studies have shown greater activation in HIV-infected patients during strenuous tasks in frontal and parietal cortices, and less activation in the primary sensory cortices during rest and sensory stimulation. High-density magnetoencephalography (MEG) was utilized to evaluate the basic neurophysiology underlying attentive, visual processing in older HIV-infected adults and a matched non-infected control group. Unlike other neuroimaging methods, MEG is a direct measure of neural activity that is not tied to brain metabolism or hemodynamic responses. During MEG, participants fixated on a centrally-presented crosshair while intermittent visual stimulation appeared in their top-right visual-field quadrant. All MEG data was imaged in the time-frequency domain using beamforming. Uninfected controls had increased neuronal synchronization in the 6-12 Hz range within the right dorsolateral prefrontal cortex, right frontal eye-fields, and the posterior cingulate. Conversely, HIV-infected patients exhibited decreased synchrony in these same neural regions, and the magnitude of these decreases was correlated with neuropsychological performance in several cortical association regions. MEG-based imaging holds potential as a noninvasive biomarker for HIV-related neuronal dysfunction, and may help identify patients who have or may develop HAND. Reduced synchronization of neural populations in the association cortices was strongly linked to cognitive dysfunction, and likely reflects the impact of HIV on neuronal and neuropsychological health.
    PLoS ONE 06/2013; 8(6):e66241. DOI:10.137/journal.pone.0066241 · 3.23 Impact Factor
    • "Further support for the distinct contributions of alpha-and gamma-band oscillations toward the maintenance of relevant WM representations was obtained through the identification of the underlying cortical sources. Previous MEG studies have reported a WM load-specific strengthening of oscillatory delay activity in prefrontal and parietal areas that correlated with individual WM capacity (Palva et al., 2011), suggesting that activity in these brain areas is implicated in the maintenance of WM representations. In agreement with these findings, we report WM-related changes of gamma-band source activity in the left BA9 and the right IPL. "
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    ABSTRACT: Previous studies in electrophysiology have provided consistent evidence for a relationship between neural oscillations in different frequency bands and the maintenance of information in working memory (WM). While the amplitude and cross-frequency coupling of neural oscillations have been shown to be modulated by the number of items retained during WM, interareal phase synchronization has been associated with the integration of distributed activity during WM maintenance. Together, these findings provided important insights into the oscillatory dynamics of cortical networks during WM. However, little is known about the cortical regions and frequencies that underlie the specific maintenance of behaviorally relevant information in WM. In the current study, we addressed this question with magnetoencephalography and a delayed match-to-sample task involving distractors in 25 human participants. Using spectral analysis and beamforming, we found a WM load-related increase in the gamma band (60-80 Hz) that was localized to the right intraparietal lobule and left Brodmann area 9 (BA9). WM-load related changes were also detected at alpha frequencies (10-14 Hz) in Brodmann area 6, but did not covary with the number of relevant WM-items. Finally, we decoded gamma-band source activity with a linear discriminant analysis and found that gamma-band activity in left BA9 predicted the number of target items maintained in WM. While the present data show that WM maintenance involves activity in the alpha and gamma band, our results highlight the specific contribution of gamma band delay activity in prefrontal cortex for the maintenance of behaviorally relevant items.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 09/2012; 32(36):12411-12420. DOI:10.1523/JNEUROSCI.0421-12.2012 · 6.34 Impact Factor
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