Modes of memory: Early electrophysiological markers of repetition suppression and recognition enhancement predict behavioral performance NIKO A. BUSCH, a CHRISTIAN GROH-BORDIN, b HUBERT D. ZIMMER, b and CHRISTOPH S. HERRMANN a a Institute of Psychology, Department of Biological Psychology, Otto-von-Guericke University, Magdeburg, Germany b Department of Psychology, Brain and Cognition Unit, Saarland University, Saarbru¨ cken, Germany Abstract Different forms of perceptual memory have opposite physiological effects. Whereas repetition priming often leads to suppression of brain responses, explicit recognition has been found to enhance brain activity. We investigated effects of repetition priming and recognition memory on early gamma-band responses. In a study phase, participants performed a visual discrimination task with task-irrelevant item repetitions. Stimulus repetition suppressed early evoked gamma responses in participants with strong behavioral repetition effects. In a test phase, participants discriminated old from new items. Evoked and induced gamma activity was enhanced for old items. Effects were stronger in participants with better recognition performance. The results demonstrate a modulation of earliest stages of visual information processing by different memory systems, which is dependent on retrieval intention and predicts individual behavioral performance. Descriptors: Implicit/explicit memory, Direct/indirect memory test, Evoked gamma, Induced gamma, Memory for- mation, Memory dissociation, Repetition suppression Visual perceptual memory is revealed when behavior or phys- iological responses are altered by previous visual experience. Research on the cognitive neuroscience of memory has provided abundant evidence that memory is not a unitary function, but can be subdivided into several functionally and anatomically different subcomponents. A common distinction is made be- tween implicit versus explicit memory processes. Explicit mem- ory is revealed in so–called direct tasks, in which performance on a task requires intentional retrieval of previous experiences. For example, in recognition memory paradigms, participants per- form old/new judgments of learned and novel items. In contrast, implicit memory is often inferred from indirect tasks that mea- sure behavioral or physiological effects of previous experiences in a task that does not require conscious or intentional retrieval of those experiences (Schacter & Buckner, 1998; Schacter, Dob- bins, & Schnyer, 2004). One widely studied form of implicit memory is repetition priming: the facilitation of behavioral responses caused by stimulus repetition. Repetition priming is often accompanied by repetition suppression: the reduction of neurophysiological responses to repeated stimuli (Buckner & Koutstaal, 1998; Grill-Spector, Henson, & Martin, 2006). An influential view is that priming and recognition are mediated by functionally independent and neurally distinct memory systems (Donaldson, Petersen, & Buckner, 2001; Groh-Bordin, Zimmer, & Mecklinger, 2005; Mecklinger, 2000; Paller, Hutson, Miller, & Boehm, 2003; Rugg et al., 1998; Voss & Paller, 2006). Repetition suppression has been found in several early visual areas (Buckner & Koutstaal, 1998; Grill-Spector et al., 2006), and under certain circumstances even near striate cortex (Vuilleumier, Schwartz, Duhoux, Dolan, & Driver, 2005), whereas increased neuronal activity in sensory areas has been associated with explicit recog- nition (Nyberg, 2006; Wheeler, Petersen, & Buckner, 2000). Moreover, double dissociations between priming and recogni- tion memory in different types of amnesic patients have been reported by Keane, Gabrieli, Mapstone, Johnson, and Corkin (1995). In that study, priming was impaired in a patient with bilateral occipital-lobe lesions who had no deficit in visual rec- ognition memory. A patient with bilateral medial temporal lobe lesions showed the reversed pattern of deficits. This dissociation suggests that the processes underlying recognition memory and perceptual priming are functionally and neurally separable. In the study by Schott et al. (2005), response decreases for primed items in the absence of explicit retrieval were found in bilateral occipital and inferior temporal cortex. In contrast, explicit retrieval activated separate areas in parietal, temporal, and pre- frontal cortex. It should be noted, however, that other studies This study was supported by the German Research Foundation (DFG, grants HE 3353/2-2 and Zi 308/4-2). The authors thank Thorsten Brinkmann for creating the stimuli and Anke Dudeck, Stefanie Thaerig, and Daniel Lenz for help during data acquisition. We also thank Till Schneider for his helpful suggestions and Luita Spangler and Katie Ziehr for their comments on an earlier version of this manuscript. Address reprint requests to: C.S. Herrmann, Institute of Psychology, Department of Biological Psychology, Otto-von-Guericke University, PO-Box 4120, 39016 Magdeburg, Germany. E-mail: christoph.herrmann @nat.uni-magdeburg.de Psychophysiology, 44 (2007), **–**. Blackwell Publishing Inc. Printed in the USA. Copyright r 2007 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2007.00607.x 1