erations, respectively; and (iii) left posterior/ventral (Broca's area) and bilateral posterior/dorsal areas were more activated during WM than during ER, possibly reflecting phonological and generic WM operations, respectively. Second, hippocampal and parahippocampal regions were activated not only for ER but also for WM. This result suggests that indexing operations mediated by the medial temporal lobes apply to both long-term and short-term memory traces. Overall, our results show that direct cross-function comparisons are critical to understand the role of different brain regions in various cognitive functions. 2002 Elsevier Science (USA) INTRODUCTION During the past decade, numerous positron emission tomography (PET) and functional MRI (fMRI) studies have investigated the neural correlates of different cognitive functions (for a review, see Cabeza and Nyberg, 2000). Although most studies have focused on a single function (see however, LaBar et al., 1999; Braver et al., 2001; Ny

Two imaging studies were performed -- one of an algebraic transformation task studied by Anderson, Reder, and Lebiere (1996) and the other of an abstraction symbol manipulation task studied by Blessing and Anderson (1996). ACT-R models exist that carefully model the latency patterns in these tasks. These models require activity of an imaginal buffer to represent changes in the problem representation, in a retrieval buffer to hold information from declarative memory, and in a manual buffer to hold information about motor behavior. A general theory is described about how to map activity in these buffers onto the fMRI bold response. This theory claims that the BOLD response is integrated over the duration a buffer is active and can be used to predict the observed BOLD function. Activity in the imaginal buffer is shown to predict the BOLD response in a left, posterior parietal region; activity in the retrieval buffer is shown to predict the BOLD response in a left DLPFC region; and activity in the manual buffer is shown to predict activity in a motor region. Cognitive models have been increasingly successful at accounting for complex data sets on problem-solving (Anderson & Lebiere, 1998; Meyer & Kieras, 1997; Pew & Mavor, 1998). Largely, these cognitive models have focused on reaction time and accuracy and usually only final times and accuracies. These models often specify rather complex sequences of unseen processes taking place over many seconds. Even when the pattern of data they fit is correspondingly complex, one is naturally wary about a chain of inferences about unseen processes. It would be better if we could have data about these intervening processes. Basically, more converging data would be better. This paper will demonstrate the potential of functional magnetic...

Novel lists of 7 +/- 2 known items can be reliably stored in an oscillatory short-term memory network: interaction with long-term memory.

For cognitive neuroscience to go forward a more explicit effort is needed to use neurophysiology to constrain how the brain produces human mental functions. This review begins with the suggestion that two fundamental features may be critical for this effort. The first is the connectivity of the brain, which occupies an intermediate position between complete redundant interconnections and independence. The term semiconnected is presented as a designation, which is an obvious derivation of the term semiconductors as used in engineering. The second is transient response plasticity where a given neuron or collection of neurons may show rapid changes in response characteristics depending on experience. Response plasticity is a ubiquitous property of the brain rather than a unique characteristic of "neurocognitive" regions. These two properties may be brought together when brain areas interact such that their aggregate function embodies cognition. Three examples are used to illustrate these ...

steriodorsal medial parietal areas were specifically involved in retrieval of spatial context compared to retrieval of nonspatial context. The posterior activations are consistent with a model of long-term storage of allocentric representations in medial temporal regions with translation to body-centered and head-centered representations computed in right posterior parietal cortex and buffered in the temporoparietal pathway so as to provide an imageable representation in the precuneus. Prefrontal activations are consistent with strategic retrieval processes, including those required to overcome the interference between the highly similar events. 2001 Academic Press INTRODUCTION Memory for the events we experience as we move around our environment is fundamental to normal functioning in daily life. This type of memory is often referred to as "episodic" (Tulving, 1983) and is crucially dependent on the medial temporal lobes (Scoville and Milner, 1957; A

Brain imaging methods, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), provide a unique opportunity to study the neurobiology of human memory. Since these methods can measure most of the brain, it is possible to examine the operations of large-scale neural systems and their relation to cognition. Two neuroimaging studies, one concerning working memory and the other episodic memory retrieval, serve as examples of application of two analytic methods that are optimized for the quantification of neural systems, structural equation modeling and partial least squares. Structural equation modeling was used to explore shifting prefrontal and limbic interactions from the right to the left hemisphere in a delayed match-to-sample task for faces. A feature of the functional network for short delays was strong right hemisphere interactions between hippocampus, inferior prefrontal, and anterior cingulate cortices. At longer delays, these same three areas were strongly linked, but in the left hemisphere, which was interpreted as reflecting change in task strategy from perceptual to elaborate encoding with increasing delay. The primary manipulation in the memory retrieval study was different levels of retrieval success. Partial least squares was used to determine whether the image-wide pattern of covariances of Brodmann areas 10 and 45/47 in right prefrontal cortex (RPFC) and the left hippocampus (LGH) could be mapped on to retrieval levels. Area 10 and LGH showed an opposite pattern of functional connectivity with a large expanse of bilateral limbic cortices that was equivalent for all levels of retrieval as well as the baseline task. However, only during high retrieval area 45/47 was included in this pattern. The results suggest that activ...

this article now proposes that the change in hemispheric asymmetry in older adults during verbal recall is reflective of a general aging phenomenon rather than a task-specific occurrence. More specifically, under similar circumstances, PFC activity during cognitive performances tends to be less lateralized in older adults than in younger adults. This empirical generalization is conceptualized in terms of a model called hemispheric asymmetry reduction in older adults (HAROLD)

Adult age differences are frequently observed in the performance of memory tasks, but the changes in neural function mediating these differences are largely unknown. We used H 2 O positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) during Encoding, Baseline, and Retrieval conditions of a recognition memory task. Twelve young adults (20--29 years) and 12 older adults (62--79 years) participated. During each task condition, participants made a two-choice manual response to each of 64 words. Analyses of the performance data yielded evidence of age-related slowing of encoding and retrieval processes, and an age-related decline in the accuracy of yes/no recognition (d'). The rCBF activation associated with both encoding and retrieval was greater for older adults than for young adults, but this pattern was more clearly evident for memory retrieval. For young adults, rCBF activation during retrieval occurred primarily in right prefrontal cortex, whereas older adults exhibited a more bilateral pattern of prefrontal activation. Regression analyses predicting reaction time in the memory task from regional PET counts confirmed that the neural system mediating memory retrieval is more widely distributed for older adults than for young adults. Both age groups exhibited some decrease in rCBF activation in the second half of the test session, relative to the first half. The practice-related decrease in rCBF activation was more prominent for young adults, suggesting that the older adults' recruitment of additional neural systems reflects a more continual allocation of attention to support task performance. Hum. Brain Mapping 7:115--135, 1999. # 1999 Wiley-Liss, Inc.

studies, which offer higher spatial resolution, will shed new light on when and why encoding yields subsequent remembering. Keywords: subsequent memory effect; episodic encoding; episodic memory; event-related potentials; fMRI; PET 1. INTRODUCTION In the course of a typical day, humans experience many complex events: perceiving faces and other objects, reading words and text passages, interpreting the meaning of spoken phrases, and the like. Yet, at the end of the day, only a subset of these experiences are memorable, with many of the day's events having been forgotten. To understand human memory, it is critically important to determine why some experiences can be later remembered, whereas others are subsequently forgotten. Considerable behavioural and neuropsychological evidence indicates that the ability to remember a given experience is affected by many factors, including the kinds of processing operations that are engaged at the time of encoding and retrieval, and interactions

The purpose of this study was to identify the brain regions invoked when subjects attempt to learn verbal materials for a subsequent memory test. Twelve healthy subjects undertook two different tasks: reading and encoding of word pairs, while they were being scanned using [150]H20 positron emission tomography (PET). As expected, the encoding pairs were remembered much better (recall 39% vs. 8%; P < 0.001) than reading pairs in a subsequent memory test. The encoding scans, as compared to reading scans, showed activation of the left prefrontal cortex, the anterior cingulate cortex and the left medial temporal cortex. The left prefrontal activations were in two discrete regions: (i) a left anterior and inferior left prefrontal (Brodmann's areas 45, 46) which we attribute to semantic processing; and (ii) a left posterior mid-frontal region (BA 6, 44) which may reflect rote rehearsal. We interpret the data to suggest that when subjects use cognitive strategies of semantic processing and rote-rehearsal to learn words, they invoke discrete regions of the left prefrontal cortex. And this activation of the left prefrontal cortex along with the medial temporal region leads to a neurophysiological memory trace which can be used to guide subsequent memory retrieval.