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The Functional Role of Theta Band Activity in Visuospatial Working MemoryJanina Jochim1, Eelke Spaak1, Lisa Lin2, & Mark Stokes1
Contact: [email protected]
Introduction
Task
1 Department of Experimental Psychology, University of Oxford 2 Department of Psychiatry, University of California, San Franscisco, United States
Start Memory Items Delay Probe
300 ms100 ms
Response Feedback
20 ms
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Participants (n = 20) were presented with either two (low-load condition) or four (high-load condition) different shapes. After a delay period of three seconds, one of the stimuli re-occured at the centre of the screen and participants indicated the location in which they had previously seen this shape. EEG recordings were taken from 60 scalp-electrodes.
FzF1 F2
Results
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Recent electroencephalogram (EEG) studies suggest that neural oscillations at the theta band (4-8 Hz) recorded at frontal electrodes (e.g., Fz) are involved in active maintenance of working memory (WM) information (e.g., Roberts, Hsieh, & Ranganath, 2013).
In rodents, frontal theta seems to occur at specific phase of hippocampal theta oscillations (e.g., Gordon, 2011). In humans, hippocampal theta increases with working memory load (Axmacher et al., 2010).
Theta distribution Electrodes of interest: Fz, F1, F2
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Conclusion
ReferencesAxmacher, N., Henseler, M. M., Jensen, O., Weinreich, I., Elger, C. E. & Fell, J. (2010). Cross-frequency coupling supports multi-item working memory in the human hippocampus. Proc Natl Acad Sci, 107(7), p.3228-3233; Gordon, J. A. (2011). Oscillations and hippocampal-prefrontal synchrony. Current Opinion in Neurobiology, 21, p. 486 - 491; Hsieh, L.-T., Ekstrom A.D., & Ranganath, C. (2011). Neural oscillations associated with item and temporal order maintenance in working memory. Journal of Neuroscience, 31, p. 10803-10810; Lisman, J.E., & Jensen, O. (2013). The theta-gamma neural code. Neuron, 77, p.1002-1016; Roberts, B. M., Hsieh, L.-T., & Ranganath, C. (2013). Oscillatory activity during maintenance of spatial and temporal information in working memory. Neuropsychologia, 51, p.349-357.
Objectives: The current study aimed to find out if FMT increases with load even in the absence of a sequential component in order to clarify thefunctional significance of theta in human memory processes.
It has been speculated that frontal midline theta (FMT) provides a mechanism through which the sequence order between individual items is retained in memory (e.g., Hsieh, Ekstrom, & Ranganath, 2011; Lisman & Jensen, 2013).
Theta power increased with memory load during the delay
Delay period theta power did not vary with accuracy or reaction time High memory load
Rea
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n t
ime
(s)
-1 0 1 2 3 4 5 6 7
-1 0 1 2 3 4 5 6 7
Low memory load
Low memory load
0.970.965
0.96
0.955
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0.945
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High Theta
Low Theta
0.530.5250.520.5150.510.5050.50.495
Acc
ura
cy
-1 0 1 2 3 4 5 6 7
0.8750.87
0.865
0.855
0.85
0.845
0.84
0.86
High Theta
Low Theta
Time (s)
Time (s) Time (s)
High memory load
0-1 1 2 3 4 5 6 7
0.7850.780.7750.770.7650.760.7550.750.7450.74
Time (s)
Contrast between high vs. low load shows significant differences over the frontal lobe.
(unpublished hippocampal data)
The present study shows that FMT power increases with the number of items maintained in WM even when these items are not presented sequentially. This suggests that FMT does not necessarily reflect the maintenance of temporal order of memory items.
Our results suggest that FMT could reflect the number of items in visuospatial WM, however power in the delay period did not vary with WM performance.
Therefore, it remains possible that FMT simply reflects task difficulty. Further research is required to pinpoint the role of FMT in WM.
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n t
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(s)
Acc
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Mean (Fz, F1, F2)/1
High Load Low Load
Delay
