Decreased parahippocampal activity in associative priming: Evidence from an event-related fMRI study

Abstract

In recent years, there has been intense debate on the neural basis of associative priming, particularly on the role of the medial temporal lobe (MTL) in retrieving associative information without awareness. In this study, event-related fMRI was used while healthy subjects performed a perceptual identification task on briefly presented unrelated word pairs and an associative recognition memory task. Contamination of priming by explicit memory was successfully controlled, as associative priming and explicit memory were dissociated on the behavioral level. The fMRI results showed a functional dissociation within the MTL with respect to associative priming effects. The right parahippocampal cortex, but not the hippocampus, showed decreased activation for old vs. new pairs and old vs. recombined pairs (associative priming). The bilateral hippocampus and the right parahippocampal cortex were involved in explicit associative memory. These data provide evidence that subregions of the MTL participate in associative priming even when explicit involvement was controlled. Thus, different regions within the MTL play distinct roles in explicit and implicit associative memory.

Sustained activity within the default mode network during an implicit memory task

“…For example, the occipital cortex, bilateral fusiform gyrus, the prefrontal cortex, and the medial temporal lobe (MTL) showed significant above-baseline activation for word pairs. In addition, we found functional dissociations between subregions of the MTL in implicit and explicit tasks, showing that the parahippocampal region was more activated in the associative priming task, and both the parahippocampal and hippocampus were activated in the associative recognition task (for details, see Yang et al, 2008). …”

“…The activation results are reported in a separate paper (Yang et al, 2008), and the deactivation results are reported in detail in this paper. Some regions were activated for different types of word pairs, in both implicit and explicit tasks.…”

The role of the parahippocampal cortex in cognition

“…It is relevant to keep in mind that an episode is associative in nature, linking objects, relations, places, sounds, and more, in a single compounded construct. Indeed, associative memory, the memory that links different items together (e.g., face-name), rather than memory for a single item, is found to activate the PHC [14,39,44-49]. Thus, the PHC is not involved in just any type of episodic memory, but memory-related processing that involves associations between elements.…”

Dissociable Forms of Repetition Priming: A Computational Model

“…In the hippocampus and surrounding medial temporal lobe (MTL) cortices, this effect is often found related to "expectation violations" in which both novel (i.e., random) and familiar sequences of spatial or temporal patterns yield a low neural response, whereas patterns that explicitly violate known expectations lead to a large response (associative novelty). For example, Yang et al (2008) provided evidence based on fMRI human research where the right parahippocampal cortex showed increased activation for unexpected stimulus pairs. Schott et al (2004) and, independently, Düzel, Habib, Guderian, andHeinze (2004) presented results where participants distinguished between familiar and novel configurations of pairs of items.…”

“…The priming phenomenon is tied in with the changing of neural activity in different cortical areas (Gotts, 2003;Schacter, Wig, & Stevens, 2007;Wig, Grafton, Demos, & Kelley 2005;Wiggs & Martin, 1998;Soldan, Habeck, Gazes, & Stern, 2010;Voss & Paller, 2010;GrillSpector, Henson, & Martin, 2006). In particular, there is much evidence that the repetition of a stimulus (stimulus novelty) triggers changes in neural activity in the perirhinal and lateral entorhinal area, while novel temporal or special arrangement of objects (associative novelty) affects the activity in the parahippocampal (postrhinal) cortex as well as in the hippocampus (Wan, Aggleton, & Brown, 1999;Eichenbaum, Yonelinas, & Ranganath, 2007;Brown & Aggleton, 2001;Yang, Meckingler, Xu, Zhao, & Weng, 2008).…”