Cross-frequency coupling during human memory processes: evidence from intracranial EEG
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1
Dept. of Epileptology, University of Bonn, Germany
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2
Donders Centre for Cognitive Neuroimaging, United Kingdom
Individual sensory stimuli are represented by assemblies of neurons synchronized in the gamma frequency range (25–100 Hz). The same has been suggested for individual contents of working memory (WM) as long as they are not yet transferred into long-term memory. More than one item can be maintained simultaneously in WM, and thus interference between multiple items must be avoided. According to an influential computer model, maintenance of multiple items is accomplished by neural assemblies synchronized in the gamma frequency range that are locked to consecutive phase ranges of oscillatory activity in the theta frequency range (4–8 Hz). Here, I will present experimental evidence for this model based on intracranial EEG data of human epilepsy patients. These data show that simultaneous maintenance of multiple items in WM is accompanied by cross-frequency coupling of oscillatory activity in the hippocampus, which is recruited during multi-item WM. Furthermore, maintenance of an increasing number of items was associated with shifts of the modulation maxima to lower frequencies: While modulation was maximal at 30 Hz to 7.5 Hz during maintenance of one item, it was maximal at 25 Hz to 6.4 Hz during maintenance of four items. Thus, the ratio of these frequencies remained constant at around 4. Possibly, this number is related to the number of items that can be maintained simultaneously, i.e., to the WM capacity. To summarize, our data support the idea that working memory in humans depends on a neural code using phase information. Funding: German Research Foundation, SFB TR-3.
Keywords:
Cross-frequency coupling,
intracranial EEG
Conference:
XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011.
Presentation Type:
Symposium: Oral Presentation
Topic:
Symposium 18: The cognitive role of cross-frequency coupling
Citation:
Axmacher
N,
Henseler
M,
Jensen
O and
Fell
J
(2011). Cross-frequency coupling during human memory processes: evidence from intracranial EEG.
Conference Abstract:
XI International Conference on Cognitive Neuroscience (ICON XI).
doi: 10.3389/conf.fnhum.2011.207.00575
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Received:
14 Nov 2011;
Published Online:
28 Nov 2011.
*
Correspondence:
Dr. Nikolai Axmacher, Dept. of Epileptology, University of Bonn, Bonn, Germany, nikolai.axmacher@rub.de