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1) Phase and amplitude dynamics of cortical oscillations during working memory task performance 2) Neural oscillations, slow fluctuations, and human perceptual performance.
  CBN (Computational Biology and Neurocomputing) seminars

Friday 24 September 2010
from 10:00 to 12:00
at RB35
Speaker : Satu Palva and Matias Palva (University of Helsinki)
Abstract : 1) Visual working memory (VWM) is based on sustained neuronal activity in a complex cortical network of frontal, parietal, occipital, and temporal areas. The neuronal mechanisms that coordinate this distributed processing to sustain coherent mental images have remained unknown. Local and inter-areal neuronal synchronization may, nevertheless, be relevant in this context. We mapped the anatomical and dynamic structures of network synchrony supporting VWM by using a neuroinformatics approach and combined magnetoencephalography and electroencephalography [0]. We also characterized evoked responses and oscillation amplitude dynamics. Interareal phase synchrony was sustained and stable during the VWM retention period among frontoparietal and visual areas in α- (10–13 Hz), β- (18–24 Hz), and γ- (30–40 Hz) frequency bands. Furthermore, retention period synchronization was strengthened with increasing memory load among the frontoparietal regions known to underlie executive and attentional functions during memory maintenance. On the other hand, the subjects’ individual behavioral VWM capacity was predicted by synchrony in a network in which the intraparietal sulcus was the most central hub. Interestingly, however, we observed that while the 120-ms-evoked-response component was linearly dependent on memory load, the 170-ms component plateaued at around 4 objects and was correlated with individual VWM capacity. These data thus indicate that subsets of both the VWM encoding- and retention-period activities predict individual behavioral performance. We suggest that interareal phase synchrony in the α-, β-, and γ-frequency bands among frontoparietal and visual regions could be a systems level mechanism for coordinating and regulating the maintenance of neuronal object representations in VWM. 2) Human behavioral performance fluctuates over time in a scale-free fashion. This effect is particularly salient for threshold-level stimuli that sometimes are consciously perceived and sometimes not, even though the stimuli remain physically identical. Several recent studies shed light on the neuronal underpinnings of these performance fluctuations and show that neuronal oscillations in a wide range of frequency bands play a role in regulating the activity of cortical networks. Utilizing full-band electroencephalography (EEG), Monto et al showed that the detection of somatosensory threshold-level stimuli was locked to the phase of infraslow EEG fluctuations in the frequency range of 0.01 to 0.1 Hz [1]. The phase of infraslow fluctuations was also correlated with the amplitude of faster EEG activities in the frequency band from 1 to 40 Hz. Similar effects characterize faster oscillations as well: in a number of cognitive tasks, the phase of ongoing oscillations in the delta- (1-4 Hz), theta- (4-8 Hz) and alpha- (8-14 Hz) frequency bands is correlated with the amplitude of faster oscillations [2, 3] and with behavioral [2] and perceptual [4] performance. Thus, the phases of the infraslow-, delta-, theta-, and alpha-frequency band oscillations reflect hierarchically nested excitability windows in cortical networks. In this presentation, I discuss the putative links among neural oscillations, slow fluctuations, and human perceptual performance. [0] Palva JM, Monto S, Kulashekhar S, Palva S (2010) Proc Natl Acad Sci USA 10.1073/pnas.0913113107 [1] Monto S, Palva S, Voipio J, Palva JM (2008) J Neurosci 28:8268-8272. [2] Lakatos P, Karmos G, Mehta AD, Ulbert I, Schroeder CE (2008) Science 320:110-113. [3] Canolty RT, et al. (2006) Science 313:1626-1628. [4] Busch NA, Dubois J, VanRullen R (2009) J Neurosci 29:7869-7876.

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