Reading Group: Investigating the temporal dynamics of long-term memory representation retrieval

SpeakerTom Diethe
AffiliationBritish Medical Association
DateWednesday, 04 Apr 2012
Time16:00 - 17:00
LocationFoster Court 235
Event seriesMachine Learning for Neuroimaging Reading Group

Investigating the temporal dynamics of long‐term memory representation
retrieval using multivariate pattern analyses on magnetoencephalography data

It is generally accepted that long‐term memory (LTM) representations are synaptically encoded in the
brain. The temporal dynamics of retrieval of these LTM representations however, remain to be
elucidated. In the current study, we utilize multivariate pattern analyses (MVPA) on
magnetoencephalography (MEG) data of a paired‐associate recall task, where pictures of objects are
randomly paired to different types of gratings. By training and testing a classifier algorithm on data
segments of the recall interval, we attempt to predict the orientation or color of the grating being
recalled by the subject, on a trial‐by‐trial bases. We consistently observe an increase in classification
accuracy at around 500 milliseconds after object cue presentation, albeit not statistically significant on
the group level. Exploratory analyses of the topographic plots of classifier parameters reveal that data
from posterior sensors contain the most informative features for the purpose of classification. This
observed importance of posterior regions may relate to a previously reported positive ERP component
during a paired‐associate recall task. If so, results from our study suggest that this ERP component
concerns processing of representational information and possibly reflects the macroscopic aggregate of
so‐called pair‐coding neurons, earlier observed in monkey inferior temporal cortex. Moreover, clusters
of frontal sensors also appear to be important for classification at some time intervals. The reported
existence of pair‐coding neurons in monkey prefrontal cortex may be related to this observed
importance of frontal regions. Additionally, frontal regions may be involved in learning strategies and
associated language processes. In conclusion, our exploratory MPVA of MEG data provides some
support for temporally specific neurophysiological processes underlying LTM retrieval during paired‐
associate recall.

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