Trial-by-Trial Hippocampal Encoding Activation Predicts the Fidelity of Cortical Reinstatement During Subsequent Retrieval.

According to current models of episodic memory, the hippocampus binds together the neural representation of an experience during encoding such that it can be reinstated in cortex during subsequent retrieval. However, direct evidence linking hippocampal engagement during encoding with subsequent cortical reinstatement during retrieval is lacking. In this study, we aim to directly test the relationship between hippocampal activation during encoding and cortical reinstatement during retrieval.

The neural correlates of competition during memory retrieval are modulated by attention to the cues.

As people learn more facts about a concept, those facts become more difficult to remember. This is called the fan effect, where fan refers to the number of facts known about a concept. Increasing fan has been shown to decrease accuracy and increase response time and left ventrolateral prefrontal cortex (VLPFC) activity during retrieval.

The ghosts of brain states past: remembering reactivates the brain regions engaged during encoding.

There is growing evidence that the brain regions involved in encoding an episode are partially reactivated when that episode is later remembered. That is, the process of remembering an episode involves literally returning to the brain state that was present during that episode. This article reviews studies of episodic and associative memory that provide support for the assertion that encoding regions are reactivated during subsequent retrieval.

Early neural signatures of visual short-term memory.

Visual short-term memory (VSTM) relies on a distributed network including sensory-related, posterior regions of the brain and frontal areas associated with attention and cognitive control. To characterize the fine temporal details of processing within this network, we recorded event-related potentials (ERPs) while human subjects performed a recognition-memory task. The task's difficulty was graded by varying the perceptual similarity between the items held in memory and the probe used to access memory.

Characterizing the ERP Old-New effect in a short-term memory task.

The early and late components of the event-related potential (ERP) Old-New effect are well characterized with respect to long-term memory, and have been associated with processes of familiarity and recollection, respectively. Now, using a short-term memory paradigm with verbal and nonverbal stimuli, we explored the way that these two components respond to variation in recency and stimulus type. We found that the amplitude of the early component (or frontal N400, FN400) showed Old-New effects only for verbal stimuli and increased with recency.

A rational account of memory predicts left prefrontal activation during controlled retrieval.

What is the role of the left prefrontal cortex in the controlled retrieval of learned information? We present a theory of declarative retrieval that posits that the amount of control exerted by this region during retrieval is inversely proportional to 1) the frequency and recency of previous experiences with the retrieved memory and 2) the associative strength between the current context and the retrieved memory. This theory is rational in the sense that it claims that declarative retrieval is highly sensitive to the statistical regularities in the environment. We demonstrate how our theory produces precise predictions of response time and neural activity during recall and test these predictions in an experiment that manipulates the frequency of previous experiences and the associative strength to the retrieval cues.

Quantitative regional cerebral blood flow MRI of animal model of attention-deficit/hyperactivity disorder.

The spontaneously hypertensive rat (SHR) has been widely used as an animal model for attention-deficit/hyperactivity disorder (AD/HD), a developmental disorder that affects 3-5% of school-age children. Quantitative high-resolution (180 x 180 x 1500 microm) perfusion magnetic resonance imaging was performed to evaluate regional CBF in AD/HD rats (SHR, n=7) and control Wistar Kyoto rats (WKY, n=9) in the frontal cortex, motor cortex, sensory cortex, corpus callosum, hippocampus, thalamus, globus pallidus, caudoputamen and whole brain. The accuracy of repeated cerebral blood flow (CBF) measurements within animals in these brain regions ranged from 3% to 10% (7 repeated measures) and across animals ranged from 15% to 18% (n=7 rats), respectively, indicating highly accurate and reproducible CBF measurements.

The roles of prefrontal and posterior parietal cortex in algebra problem solving: a case of using cognitive modeling to inform neuroimaging data.

In naturalistic algebra problem solving, the cognitive processes of representation and retrieval are typically confounded, in that transformations of the equations typically require retrieval of mathematical facts. Previous work using cognitive modeling has associated activity in the prefrontal cortex with the retrieval demands of algebra problems and activity in the posterior parietal cortex with the transformational demands of algebra problems, but these regions tend to behave similarly in response to task manipulations (Anderson, J.R.