Academic journal article Cognitive, Affective and Behavioral Neuroscience

Posterior Parietal Cortex Activity Predicts Individual Differences in Visual Short-Term Memory Capacity

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Posterior Parietal Cortex Activity Predicts Individual Differences in Visual Short-Term Memory Capacity

Article excerpt

Humans show a severe capacity limit in the number of objects they can store in visual short-term memory (VSTM). We recently demonstrated with functional magnetic resonance imaging that VSTM storage capacity estimated in averaged group data correlated strongly with posterior parietal/superior occipital cortex activity (Todd & Marois, 2004). However, individuals varied widely in their VSTM capacity. Here, we examined the neural basis of these individual differences. A voxelwise, individual-differences analysis revealed a significant correlation between posterior parietal cortex (PPC) activity and individuals' VSTM storage capacity. In addition, a region-of-interest analysis indicated that other brain regions, particularly visual occipital cortex, may contribute to individual differences in VSTM capacity. Thus, although not ruling out contributions from other brain regions, the individual-differences approach supports a key role for the PPC in VSTM by demonstrating that its activity level predicts individual differences in VSTM storage capacity.

Our ability to grab onto and hold in mind the information presented in a visual scene is extremely limited. For instance, subjects have great difficulty in detecting a gross change between two similar scenes if these scenes are separated in time or by another visual stimulus (Rensink, 2002; Rensink, O'Regan, & Clark, 1997; Simons, 1996). Although the earliest stages of visual information processing are endowed with virtually unlimited processing capacities (Pashler, 1988; Phillips, 1974; Sperling, 1960), severe limits occur when the visual information is stored into visual working memory, which can at best accommodate four visual items (Cowan, 2001; Luck & Vogel, 1997; Pashler, 1988; Vogel, Woodman, & Luck, 2001). This bottleneck of information processing has significant real-life consequences, since it is considered to limit what information can be explicitly perceived and acted upon (Becker, Pashler, & Anstis, 2000; Chun & Potter, 1995; Jolicoeur, Dell'Acqua, & Crebolder, 2001 ; Rensink, 2002; Shapiro, Arnell, & Raymond, 1997).

Due to the ubiquitous role of working memory in visual cognition, it is not too surprising that it has been associated with a large network of brain regions in both humans (J. D. Cohen et al., 1997; Courtney, Ungerleider, Keil, & Haxby, 1997; Jonides et al., 1993; Linden et al., 2003; Munk et al., 2002; Pessoa, Gutierrez, Bandettini, & Ungerleider, 2002; Sala, Rämä, & Courtney, 2003) and nonhuman primates (Chafee & Goldman-Rakic, 1998; Constantinidis & Steinmetz, 1996; Funahashi, Bruce, & Goldman-Rakic, 1989; Fuster, 1990; Goldman-Rakic, 1996; Miller & Desimone, 1994; Quintana & Fuster, 1999). Encompassing all the cortical lobes, this network can be loosely divided into regions that contribute primarily to Baddeley's (1986) central executive system and those regions involved in maintaining and storing the visual information that is manipulated by the executive system, the so-called visuospatial sketch pad (Baddeley & Logic, 1999), or visual short-term memory (VSTM).

Executive processes, such as attentional selection, control, and manipulation of information, have been associated primarily with the frontal/prefrontal cortex (Bor, Duncan, Wiseman, & Owen, 2003; Curtis & D'Esposito, 2003; Sakai, Rowe, & Passingham, 2002; Smith & Jonides, 1999). By contrast, the simple storage of sensory information in VSTM or in auditory short-term memory is thought to involve more posterior regions (Paulesu, Frith, & Frackowiak, 1993; Postle, Berger, & D'Esposito, 1999; Rowe & Passingham, 2001; Smith & Jonides, 1998). In particular, substantial evidence indicates that the posterior parietal and inferior temporal regions are involved in the retention of visual information (Munk et al., 2002; Pessoa et al., 2002; Todd & Marois, 2004). However, this anterior-posterior dissociation is likely not absolute, since the frontal/prefrontal cortex has also been involved in the simple maintenance of information (e. …

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