Encoding of novel picture pairs activates the perirhinal cortex: An fMRI study

Abstract

It is well established in nonhuman primates that the medial temporal lobe (MTL) structures, the hippocampus and the entorhinal and perirhinal cortices, are necessary for declarative memory encoding. In humans, the neuropathological and neuropsychological changes in early Alzheimer's disease (AD) further support a role for the rhinal cortex in the consolidation of new events into long-term memory. Little is known, however, regarding the function of the rhinal cortex in humans in vivo. To examine the participation of the interconnected MTL structures as well as the whole-brain network of activated brain areas in visual associative long-term memory, functional magnetic resonance imaging (fMRI) was used to determine the brain regions that are activated during encoding and retrieval of paired pictures in 12 young control subjects. The most striking finding in the MTL activation pattern was the consistent activation of the perirhinal cortex in the encoding-baseline and encoding-retrieval comparisons with a strict statistical threshold (P < 0.00001). In contrast, no perirhinal cortex activation was detected in the retrieval-baseline or retrieval-encoding comparisons even with a low statistical threshold (P < 0.05). The location of the perirhinal activation area was in the transentorhinal part of the perirhinal cortex, in the medial bank of the collateral sulcus. The hippocampus and the more posterior parahippocampal gyrus were activated in both encoding and retrieval conditions. During the encoding processing, MTL activations were more consistent and the hippocampal activation area located more anteriorly than during retrieval. The frontal, parietal, temporal, and occipital association cortices were also activated in the encoding-baseline and retrieval-baseline comparisons. The data suggest that encoding, but not retrieval, of novel picture pairs activates the perirhinal cortex. To our knowledge, this is the first fMRI study reporting encoding activation in this transentorhinal part of the perirhinal cortex, the site of the very earliest neuropathological changes in AD.

Healthy aging attenuates task-related specialization in the human medial temporal lobe

“…Our memory task evoked less position-related activity than object-related activity throughout the MTL in young subjects; whereas other studies have suggested greater activity in some MTL regions during spatial than object processing (Buffalo et al, 2006;Mitchell et al, 2000;Pihlajamäki et al, 2003Pihlajamäki et al, , 2004Pihlajamäki et al, , 2005. Our spatial memory task was relatively simple, perhaps evoking only low-level spatial memory processing in the MTL.…”

“…A number of studies have demonstrated that the medial temporal lobe (MTL) region is crucial for episodic memory function and related working memory functions (Campo et al, 2005;Habeck et al, 2005;Hannula and Ranganath, 2008;Hayes et al, 2004;Piekema et al, 2006;Ranganath et al, 2004;Yonelinas et al, 2007). In the MTL, distinct subregions have been shown to make different contributions to object and spatial memory processes (Pihlajamäki et al, 2003(Pihlajamäki et al, , 2004(Pihlajamäki et al, , 2005, in the binding of object and spatial information (Mitchell et al, 2000), in encoding and retrieval (de Zubicaray et al, 2001;Kirwan and Stark, 2004;Tsukiura et al, 2005), as well as in familiarity and recognition judgments (Daselaar et al, 2006;Gonsalves et al, 2005;Henson, 2005;Henson et al, 2005).…”

The effect of scene context on episodic object recognition: Parahippocampal cortex mediates memory encoding and retrieval success

“…Previous blocked design studies have found similar activation (regardless of subsequent memory) during intentional encoding of pairs of unrelated visual stimuli in the right parahippocampal gyrus and right hippocampus (Henke et al, 1997) and bilateral parahippocampal gyrus and hippocampus (Rombouts et al, 1997;Pihlajamaki et al, 2003). A more recent event-related fMRI study observed encoding success activity in right parahippocampal gyrus associated with correct perceptual source judgments relative to semantic source judgments, again under intentional encoding instructions (Prince et al, 2005).…”

“…Each of these topics will be addressed in more detail later, in addition to a brief discussion of the current results in relation to Multiple Trace Theory (MTT) Moscovitch, 1997, 1998;Nadel et al, 2003). , 1997) and bilateral parahippocampal gyrus and hippocampus (Rombouts et al, 1997;Pihlajamaki et al, 2003). A more recent event-related fMRI study observed encoding success activity in right parahippocampal gyrus associated with correct perceptual source judgments relative to semantic source judgments, again under intentional encoding instructions (Prince et al, 2005).…”

Rapid consolidation and the human hippocampus: Intracranial recordings confirm surface EEG

“…Although neuroimaging studies in healthy subjects have shown that the medial temporal lobe (MTL) contributes to both long-term (Milner et al, 1998;Pihlajamäki et al, 2003, Squire et al, 2004) and short-term memory (Ranganath and D'Esposito, 2001;Hannula et al, 2006;Axmacher et al, 2008), the nature of the specific MTL contributions to short-to long-term memory remains unclear. Recently, James et al (2009) explored this question in a high-density event-related potentials (ERP) study, in which healthy subjects performed a continuous recognition task of meaningful drawings.…”