ACTUALIDAD DEL NORTE DEL CAUCA

Using a variety of event-related neuroimaging methods, the neural correlates of successful episodic retrieval are mainly investigated with the ‘old / new’ paradigm (Hanslmayr et al., 2012; Rugg, 1995; Vilberg & Rugg, 2008; Wilding & Ranganath, 2010). The difference between neural activity elicited by correctly recognised studied items and correctly judged unstudied items is called the ‘old/new effect’ or retrieval-related activity. Sanquist et al. (1980) were the first group of researchers who reported an ERP old / new effect. They found that correctly recognised old items elicited significant larger positive waveforms than correctly rejected items over a parietal electrode site in a late post-stimulus time window around 450 – 750 ms. Wilding and Rugg (1996) showed that this late parietal old / new effect was associated with retrieval of source. The effect was evident only when the gender of voices of old words during

56

encoding was correctly judged. The effect between 500 and 800 ms after words onset was over left parietal sites. This effect is therefore termed the left-parietal ERP old / new effect (Rugg, 1995). It has been widely supported that the left-parietal ERP old / new effect might be an index of recollection. As an index of recollection, the amplitudes of the left-parietal old / new effect have been positively correlated with number of correct source judgments (Wilding, 2000). In addition, the effect has been found to be associated with Remember judgments but not Know judgements, or was significantly larger for Remember than Know judgments in the Remember / Know paradigm (Duarte et al., 2004; Düzel, Yonelinas, Mangun, Heinze, & Tulving, 1997). These findings suggest that the left-parietal ERP old / new effect might be related to the amount of information that can be retrieved from episodic memory.

In the study by Wilding and Rugg (1996), they found another positive-going old / new ERP effect in a later time window and over more frontal and right-lateralised scalp sites compared to the left-parietal old / new effect, which was also associated with correct source judgment. The time window of this right frontal old / new effect was from 800 ms until 1400 ms after stimulus onset. As this time window was quite close to the end of the recording epoch they used in the study, they suggested that the effects might reflect post-retrieval processes that influenced organisations of information in previous events. However, not all the studies showed a consistent result for the right frontal old/ new effect. For example, Senkfor and Petten (1998) did not find that the right frontal old/ new effect was restricted to correct source retrieval. Further, confidently recognised items without recollection have been found to elicit a right frontal old / new effect (Woodruff et al., 2006). Hayama, Johnson and Rugg (2008) showed that right-frontal old / new effects were robust for both episodic source retrieval task and semantic task on top of an old / new judgment. Therefore, compared to the

left-57

parietal old / new effect, the late right-frontal old / new effect has not been widely agreed to be related to episodic recollection.

According to dual-process models, there should be a separate neural network supporting familiarity-based recognition memory. Rugg et al. (1998) observed an earlier old / new effect before left-parietal old / new effect over frontal scalp sites. This effect started from 300 ms after stimulus onset until 500 ms. In the study, the authors also compared studied words that attracted correct judgments with new words that attracted correct judgments as a function of levels of processing. They found that from 300 ms to 500 ms, the old / new effects did not differ in levels of processing during study phase while after 500 ms, the correctly recognised words of deep processing elicited significantly more positive-going waveforms than the waveforms elicited by both correctly judged new items and correctly recognised items of shallow processing.

Therefore, they suggested that the early mid-frontal old / new effect could reflect familiarity of item recognition. Later, there are more studies supporting the idea that this mid-frontal old / new effect is different from left-parietal old / new effect in its functions and could thus be an index of familiarity (Azimian-Faridani & Wilding, 2004;

Curran, 2000; Curran & Cleary, 2003; Woodruff et al., 2006).

Functional MRI studies have also suggested that recollection and familiarity depend on different brain networks. The main idea is that increased hippocampal activity reflects recollection but not familiarity, while familiarity is positively correlated with activation of the perirhinal cortex (Diana et al., 2007). In addition, the PFC is a critical region that is thought to contribute to recollection (Simons, Owen, Fletcher, &

Burgess, 2005; Skinner, Grady, & Fernandes, 2010; Yonelinas, 2002). However, a recent study that used five-way judgments to dissociate recollection and high-confident familiarity suggested that previous findings on the role of the PFC in recollection might be attributed to high confidence in familiarity (Yonelinas et al., 2005). In the study, they

58

also proposed a network of recollection that the PPC contributes to recollection of episodic association. There is a view about the role of the PPC suggesting that it is activated by both recognised old items and false alarms compared to correct rejections and missed items (Wagner, Shannon, Kahn, & Buckner, 2005). Thus, the PPC might contribute to recollection by activating subjective experience of familiarity, which could lead to false memories.

Similarly to ERP correlates of familiarity and recollection, theta power elicited by ‘Know’ responses was larger than ‘Remember’ responses in the early time window of retrieval, while theta power was larger for ‘Remember’ responses in a later time window than ‘Know’ responses (Klimesch et al., 2001). By using a source memory paradigm, Gruber et al. (2008) found that successful source retrieval was associated with larger theta activity while larger gamma activity was related to successful item memory but not source memory. Theta activity is thought to be crucial for recollection (Düzel, Penny, & Burgess, 2010). Recently, it was found that larger theta power could predict successful source retrieval before a retrieval cue, which suggests that a better brain state for source retrieval may be reflected in a larger magnitude of theta oscillations (Addante et al., 2011).