Academic journal article Cognitive, Affective and Behavioral Neuroscience

Theta Oscillations Predict the Detrimental Effects of Memory Retrieval

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Theta Oscillations Predict the Detrimental Effects of Memory Retrieval

Article excerpt

Retrieving a target item from episodic memory typically enhances later memory for the retrieved item but causes forgetting of competing irrelevant memories. This finding is termed retrieval-induced forgetting (RIF) and is assumed to be the consequence of an inhibitory mechanism resolving retrieval competition. In the present study, we examined brain oscillatory processes related to RIF, as induced by competitive memory retrieval. Contrasting a competitive with a noncompetitive retrieval condition, we found a stronger increase in early evoked theta (4-7 Hz) activity, which specifically predicted RIF, but not retrieval-induced enhancement. Within the cognitive framework of RIF, these findings suggest that theta oscillations reflect arising interference and its resolution during competitive retrieval in episodic memory. Supplemental materials for this article may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.

Retrieval from episodic memory is constantly challenged by interference from currently irrelevant, related memory traces (Anderson & Neely, 1996; Bäuml, 2008). For example, if we want to recall what we had for dinner last week at our favorite Italian restaurant, memories related to other dinners in this restaurant interfere. To overcome such interference, the irrelevant memories are supposed to be inhibited, inducing later forgetting of the interfering information (e.g., Anderson, 2003). The aim of the present study was to identify the brain oscillatory correlates of such retrieval-induced forgetting (RIF).

In the laboratory, RIF can be investigated using the retrieval practice paradigm (Anderson, Bjork, & Bjork, 1994; Figure 1A). In this paradigm, subjects study items from different semantic categories (e.g., fruit-orange, fruit-banana, insect-ant) and subsequently repeatedly retrieve half of the items from half of the categories, using a word stem completion task (e.g., fruit-ban___). On a later memory test, the subjects are asked to recall all previously studied items. Relative to the control items from the unpracticed categories (ant), retrieval practice typically improves recall of the practiced material (banana) but impairs recall of the unpracticed material (orange), which is referred to as the RIF finding (for reviews, see Anderson, 2003; Bäuml, Pastötter, & Hanslmayr, 2010).

It is widely assumed that RIF is caused by inhibitory processes. The proposal is that during retrieval practice on a subset of the studied material, related unpracticed items interfere. To reduce the interference, the unpracticed material is inhibited by deactivation of the unpracticed items' memory representations (Anderson & Spellman, 1995). Consistently, RIF has been found across a wide range of memory tests, including cued recall tests (e.g., Anderson et al., 1994), independent-probe tests (cues not presented in a prior phase of the experiment; e.g., Anderson & Spellman, 1995), recognition tests (e.g., Spitzer & Bäuml, 2007), and implicit tests (e.g., Veling & van Knippenberg, 2004). In particular, RIF is a recall-specific effect. Accordingly, inhibitory effects of practice in episodic memory have been observed in retrieval practice conditions, but not when a subset of the material was reexposed or learned on a second instance (Bäuml & Aslan, 2004; Ciranni & Shimamura, 1999; for related results, see Anderson, Bjork, & Bjork, 2000; Bäuml, 2002).

Investigating the neural mechanisms mediating RIF, two recent studies compared neural activity in a retrieval practice condition with neural activity in a reexposure condition (Johansson, Aslan, Bäuml, Gäbel, & Mecklinger, 2007; Wimber, Rutschmann, Greenlee, & Bäuml, 2009). Using electrophysiological measures of brain activity, Johansson et al. observed increased sustained positivity over frontal electrode sites during the retrieval practice phase, which predicted later forgetting. Using fMRI, Wimber et al. …

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