Decoding oscillatory representations and mechanisms in memory.

A fundamental goal in memory research is to understand how information is represented in distributed brain networks and what mechanisms enable its reactivation. It is evident that progress towards this goal will greatly benefit from multivariate pattern classification (MVPC) techniques that can decode representations in brain activity with high temporal resolution. Recently, progress along these lines has been achieved by applying MVPC to neural oscillations recorded with electroencephalography (EEG) and magnetoencephalography (MEG). We highlight two examples of methodological approaches for MVPC of EEG and MEG data that can be used to study memory function. The first example aims at understanding the dynamic neural mechanisms that enable reactivation of memory representations, i.e., memory replay; we discuss how MVPC can help uncover the physiological mechanisms underlying memory replay during working memory maintenance and episodic memory. The second example aims at understanding representational differences between various types of memory, such as perceptual priming and conscious recognition memory. We also highlight the conceptual and methodological differences between these two examples. Finally, we discuss potential future applications for MVPC of EEG/MEG data in studies of memory. We conclude that despite its infancy and existing methodological challenges, MVPC of EEG and MEG data is a powerful tool with which to assess mechanistic models of memory.

Stimulus-response bindings code both abstract and specific representations of stimuli: evidence from a classification priming design that reverses multiple levels of response representation.

Repetition priming can be caused by the rapid retrieval of previously encoded stimulus-response (S-R) bindings. S-R bindings have recently been shown to simultaneously code multiple levels of response representation, from specific Motor-actions to more abstract Decisions ("yes"/"no") and Classifications (e.g., "man-made"/"natural"). Using an experimental design that reverses responses at all of these levels, we assessed whether S-R bindings also code multiple levels of stimulus representation. Across two experiments, we found effects of response reversal on priming when switching between object pictures and object names, consistent with S-R bindings that code stimuli at an abstract level. Nonetheless, the size of this reversal effect was smaller for such across-format (e.g., word-picture) repetition than for within-format (e.g., picture-picture) repetition, suggesting additional coding of format-specific stimulus representations. We conclude that S-R bindings simultaneously represent both stimuli and responses at multiple levels of abstraction.

Priming, response learning and repetition suppression.

Prior exposure to a stimulus can facilitate its subsequent identification and classification, a phenomenon called priming. This behavioural facilitation is usually accompanied by a reduction in neural response within specific cortical regions (repetition suppression, RS). Recent research has suggested that both behavioural priming and RS can be largely determined by previously learned stimulus-response associations. According to this view, a direct association forms between the stimulus presented and the response made to it. On a subsequent encounter with the stimulus, this association automatically cues the response, bypassing the various processing stages that were required to select that response during its first presentation. Here we reproduce behavioural evidence for such stimulus-response associations, and show the PFC to be sensitive to such changes. In contrast, RS within ventral temporal regions (such as the fusiform cortex), which are usually associated with perceptual processing, is shown to be robust to response changes. The present study therefore suggests a dissociation between RS within the PFC, which may be sensitive to retrieval of stimulus-response associations, and RS within posterior perceptual regions, which may reflect facilitation of perceptual processing independent of stimulus-response associations.

Jog your memory: a community screening model.

This study's objectives were to establish an annual memory-screening week, heighten public awareness of the issues surrounding cognitive impairments, promote baseline cognitive screening as part of routine examinations in primary care settings for the older adult, and detect early dementia and depression. The 264 participants completed demographic and anecdotal information and the Geriatric Depression Scale (GDS). Nurses scored the GDS and administered the Mini Mental State Examination (MMSE) and the Clock Drawing Test. Screening results and educational information were given to the participants. Results revealed that 14% of participants scored abnormally on the MMSE and approximately 14% had an abnormal GDS score.