Neural Mechanisms of Sequential Information

Marshuetz, Christy

Abstract

A number of mental disorders, such as schizophrenia, bipolar disorder and clinical depression, have long been thought to accompany deficits in working memory and frontal-lobe dysfunction (e.g. Bearden, et al., 2001; Carter, etal., 1998; Zalla, etal., 2004). Of particular difficulty for schizophrenic patients and others are executive processes such as inhibition and temporal ordering (e.g. Morice, 1990; Rossi, et al., 1997; McGrath, et al., 1997). Until recently, most researchers agreed that the frontal lobes were responsible for both inhibition and temporal ordering and that, by extension, schizophrenia was largely a frontal-lobe disorder. However, recent neuroimaging evidence suggests that the frontal lobes are not the only, nor even necessarily the most important, neural region in support of certain types of temporal information. For instance, Marshuetz, et al. (2000) have suggested that the parietal lobes play a particularly central role in working memory for sequences. Follow-up work with event-related fMRI has confirmed and extended these findings, showing that the parietal cortex is particularly sensitive to inter-item temporal distances (Marshuetz, et al., submitted). These findings, taken together with other neuroimaging studies documenting significant parietal cortex activity during the performance of both working memory and episodic long-term order memory tasks have caused researchers to reconsider the link between the parietal and prefrontal cortex, and, suggest that a dysfunction in either 1 of these areas, or the connection between them, may result in difficulty with executive functions as well as other functions, such as mental imagery and mental calculation. The fMRI studies to be proposed are aimed at better understanding the link between the parietal cortex, temporal ordering, and other cognitive processes that may rely on representations similar to those involved in remembering ordered sequences.