Functional coupling between frontal and parietal lobes during recognition memory Christopher Summer¢eld CA and Jennifer A. Mangels Psychology Department, Schermerhorn Hall, Room 406, Columbia University, 1190 Amsterdam Ave, New York, NY 10027, USA CA Corresponding Author: summerfd@psych.columbia.edu Received10 November 2004; accepted 22 November 2004 Neuroimaging studies have suggested that the frontal and parietal lobes may be important for the process by which we remember information. However, little is known about how these regions ex- change information during memory retrieval. We measured EEG synchronisation in the gamma-band (25^55 Hz), a putative mea- sure of functional coupling between brain regions, while human subjects performed a recognition memory task. Fronto-parietal synchrony was increased for true old memories relative to false memories and new items.Our results suggest that synchronization of neuronal responses in the gamma-band may be an important mechanism by which frontal and parietal regions exchange information during the recognition of past events. NeuroReport 16:117^122  c 2005 Lippincott Williams & Wilkins. Key words: DRM paradigm; Electroencephalography (EEG); False memory; Gamma-band activity (GBA); Independent components analysis (ICA); Retrieval INTRODUCTION Our understanding of how the brain distinguishes old from new events has been deepened by the advent of neuroima- ging techniques that permit trial-by-trial sorting of neural responses, such as event-related fMRI and ERP. Using these techniques, researchers have observed that neural phenom- ena that are sensitive to whether a recognition probe is old or new (‘old/new effects’) tend to be localised to the frontal and parietal lobes [1]. Further information about the neural processes underpinning recognition memory has been provided by investigations of false memory, in which subjects report recognising (with high confidence) an item to which they were not previously exposed. Interestingly, although regions of frontal cortex that show robust old/new effects do not seem to be sensitive to whether the memory is true or false [2], this is not the case for posterior brain regions, which appear to track the veridicality of the memory (‘true/false’ effects) [3–6]. Consistent with the notion that posterior brain regions are required for recollec- tion of sensory context or ‘source’, true memories may additionally involve re-activation of cortical regions that initially supported encoding of the sensory/perceptual features of the relevant stimulus (‘sensory recapitulation’) [4,5]. Whilst fMRI and ERP studies provide important informa- tion about the contribution of individual brain regions to a neural effect, other techniques are more suited to exploring how neural information is shared within a brain network during cognition. The phase-locking (coherence) of oscilla- tory neural responding between two brain regions, which may reflect functional coupling between neural assemblies, can be measured by signal processing techniques that involve decomposing the scalp EEG signal into its spectral components [7]. Initial explorations of high-frequency brain activity (gamma-band [25–55 Hz] activity or GBA) during recognition have suggested that ‘local’ synchrony over a single brain region may vary between old and new items [8], or as a function of the subjective experience which accompanies memory [9], however no study has yet explored whether long-range coherence between frontal and parietal lobes dissociates between old and new recognition or true and false recognition. In the present study, we compared both local and long-range GBA across the brain for recognition trials on which old events were judged to be old (hits) with new events judged to be new (correct rejections) and new events judged to be old (false alarms). Our data demonstrate for the first time that successful veridical recognition of visual stimuli requires long-range functional coupling between the frontal and parietal lobes, mediated in part by synchronisation of high- frequency neural responding. SUBJECTS AND METHODS Subjects: Nineteen neurologically normal right-handers (13 women; mean age 25.4 years, range 18–38 years) were paid $25 to participate in the study. All subjects gave informed consent and the study was approved by Columbia University Institutional Review Board. Design and procedure: We employed a variant of the Deese-Roediger-McDermott (DRM) task [10]. In the typical DRM task, subjects study a list of words (e.g., candy, sugar, bitterytaste) that are all semantically associated to some degree with a non-present theme word (e.g., sweet). This theme word is called the lure because the semantic overlap BRAIN IMAGING NEUROREPORT 0959-4965  c Lippincott Williams & Wilkins Vol 16 No 2 8 February 2005 117 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.