1. The Functional Role of Theta Band Activity in Visuospatial
Working Memory
Janina Jochim1
, Eelke Spaak1
, Lisa Lin2
, & Mark Stokes1
Contact: Janina.Jochim@psy.ox.ac.uk
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 ms
100 ms
Response
Feedback
20 ms
C
D K
M
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
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
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
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
Conclusion
References
Axmacher, 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 the
functional 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
Reactiontime(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
0.97
0.965
0.96
0.955
0.95
0.945
0.94
High Theta
Low Theta
0.53
0.525
0.52
0.515
0.51
0.505
0.5
0.495
Accuracy
-1 0 1 2 3 4 5 6 7
0.875
0.87
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
0.785
0.78
0.775
0.77
0.765
0.76
0.755
0.75
0.745
0.74
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.
Reactiontime(s)Accuracy
Mean (Fz, F1, F2)/1
High Load
Low Load
Delay