Expectations of Task Demands Dissociate Working Memory and Long-Term Memory Systems.

Many aspects of the complex relationship between working memory (WM) and long-term memory (LTM) remain unclear. Here, we manipulated task demands on a brief delayed-recognition paradigm to reveal behavioral and neural dissociations between these systems. Variations from a Baseline task included 3 challenges: increased delay duration, distraction during maintenance, and more closely matched memory probes, which were presented in behavioral experiments and during functional magnetic resonance imaging. Each of the challenges resulted in a significant decline in WM accuracy, and interestingly, a concurrent improvement in incidental LTM. Neural data revealed that, in task blocks, when participants anticipated, and then experienced, increased demands, they engaged medial temporal lobe (MTL) regions more during both the encoding and delay periods. Overall, these results indicate that distinct memory systems are recruited based on anticipated demands of a memory task, and MTL involvement underlies the observed dissociation between WM and LTM performance.

Induction of LTP in the human auditory cortex by sensory stimulation.

High-frequency, repetitive, auditory stimulation was used to determine whether induction of a long-lasting increase of the human auditory evoked potential (AEP) was possible. Recording non-invasively with electroencephalogram scalp electrodes, stable increases in amplitude were observed in the N1 component of the AEP, which is thought to reflect activity within auditory cortex (N1). The increase was maintained over an hour and was shown to be independent of alterations in the state of arousal. This is the first demonstration of the induction of long-lasting plastic changes in AEPs, and suggest that this represents the first direct demonstration of long-term potentiation in the auditory cortex of normal, intact humans.

Turn that frown upside down: ERP effects of thatcherization of misorientated faces.

When inverted, thatcherized faces appear normal. This may be due to a decrease in configural and an increase in featural processing. It is not known whether this processing is continuous or reflects two distinct processing systems. Using event-related potentials (ERPs), we investigated the Thatcher effect on thatcherized and normal faces at varying orientations. The ERPs paralleled the perceptual illusion. The effect of thatcherization on upright faces was visible in P1 and N170 ERP components, possibly reflecting attentional engagement due to unpleasantness of thatcherized faces. Effects were also found over two later components, the P250 component, which has been related to configural recognition, and a late parietal component possibly reflecting featural processing. The effect of thatcherization on the two later components decreased gradually (for the P250 component) and abruptly (for the late parietal component) as the faces were rotated away from the upright.