Interference effects on commonly used memory tasks

Hippocampal lesions impair non-navigational spatial memory in macaques

Decades of studies robustly support a critical role for the hippocampus in spatial memory across a wide range of species. Hippocampal damage produces clear and consistent deficits in allocentric spatial memory that requires navigating through space in rodents, non-human primates, and humans. By contrast, damage to the hippocampus spares performance in most non-navigational spatial memory tasks-which can typically be resolved using egocentric cues. We previously found that transient inactivation of the hippocampus impairs performance in the Hamilton Search Task (HST), a self-ordered non-navigational spatial search task. A key question, however, still needs to be addressed. Acute, reversible inactivation of the hippocampus may have resulted in an impairment in the HST because this approach does not allow for neuroplastic compensation, may prevent the development of an alternative learning strategy, and/or may produce network-based effects that disrupt performance. We compared learning and performance on the HST in male rhesus macaques (six unoperated control animals and six animals that underwent excitotoxic lesions of the hippocampus). We found a significant impairment in animals with hippocampal lesions. While control animals improved in performance over the course of 45 days of training, performance in animals with hippocampal lesions remained at chance levels. The HST thus represents a sensitive assay for probing the integrity of the hippocampus in non-human primates. These data provide evidence demonstrating that the hippocampus is critical for this type of non-navigational spatial memory, and help to reconcile the many null findings previously reported.

The Parahippocampal Cortex and its Functional Connection with the Hippocampus are Critical for Nonnavigational Spatial Memory in Macaques

The Hamilton Search Task (HST) is a test of nonnavigational spatial memory that is dependent on the hippocampus. The parahippocampal cortex (PHC) is a major route for spatial information to reach the hippocampus, but the extent to which the PHC and hippocampus function independently of one another in the context of nonnavigational spatial memory is unclear. Here, we tested the hypotheses that (1) bilateral pharmacological inactivation of the PHC would impair HST performance, and (2) that functional disconnection of the PHC and hippocampus by contralateral (crossed) inactivation would likewise impair performance. Transient inactivation of the PHC impaired HST performance most robustly with 30 s intertrial delays, but not when color cues were introduced. Functional disconnection of the PHC and hippocampus, but not separate unilateral inactivation of either region, also selectively impaired long-term spatial memory. These findings indicate a critical role for the PHC and its interactions with the hippocampus in nonnavigational spatial memory.

Material-specific retroactive interference effects of the Wechsler Adult Intelligence Scale-Fourth Edition on the Wechsler Memory Scale-Fourth Edition in a nonclinical sample

INTRODUCTION

This study investigated proactive and retroactive interference effects between the Wechsler Memory Scale-Fourth Edition (WMS-IV) using the flexible approach, and the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV).

METHOD

One hundred and eighty nonclinical participants were assigned to a four (visual interference, verbal interference, visual and verbal interference, vs. no interference) by two (retroactive vs. proactive) between-subjects design. The administration order of the tests was counterbalanced (i.e., administration of the WAIS-IV prior to the WMS-IV, and the WAIS-IV administered during the delay interval of the WMS-IV).

RESULTS

The WAIS-IV produced significant retroactive interference effects on the WMS-IV; however, no proactive interference effect was observed. The retroactive interference effect was dependent on material specificity.

CONCLUSIONS

The results indicate that material presented within the delay of the WMS-IV can have a significant effect on subsequent delayed recall. Clinicians should carefully consider the effects associated with carry-over effects of these tests when using them in combination.

Aging-related episodic memory decline: are emotions the key?

Episodic memory refers to the recollection of personal experiences that contain information on what has happened and also where and when these events took place. Episodic memory function is extremely sensitive to cerebral aging and neurodegerative diseases. We examined episodic memory performance with a novel test in young (N = 17, age: 21–45), middle-aged (N = 16, age: 48–62) and aged but otherwise healthy participants (N = 8, age: 71–83) along with measurements of trait and state anxiety. As expected we found significantly impaired episodic memory performance in the aged group as compared to the young group. The aged group also showed impaired working memory performance as well as significantly decreased levels of trait anxiety. No significant correlation between the total episodic memory and trait or state anxiety scores was found. The present results show an age-dependent episodic memory decline along with lower trait anxiety in the aged group. Yet, it still remains to be determined whether this difference in anxiety is related to the impaired episodic memory performance in the aged group.

Test-order effects: a measure of verbal memory influences performance on a measure of verbal fluency

In neuropsychological assessment, the impact of completing one measure on the performance of a second measure is often unknown. The current study examined the effect of a list-learning measure, the California Verbal Learning Test-Second Edition (CVLT-II), on a verbal fluency measure, the Delis-Kaplan Executive Functioning System Verbal Fluency subtest, when completed in a battery of tests. These tests were chosen because stimuli from the CVLT-II can function as responses for Verbal Fluency. Twenty-eight individuals seeking psychoeducational evaluation were randomly assigned to one of two test orders: the CVLT-II followed by Verbal Fluency, or the reverse order. Consistent with hypotheses, individuals who completed the CVLT-II first used more words from this task as responses on the various Verbal Fluency tasks, t(26) = 2.84, p = .009. In addition, they obtained higher raw scores and scaled scores on Category Fluency: t(26) = 3.01, p = .006, and t(26) = 2.53, p = .018, respectively. Surprisingly, the larger number of words produced on Category Fluency exceeded the number of CVLT-II words used as responses. These results suggest that clinicians should consider the order of administration when using these measures, and they indicate a need for further investigation of order effects.

An opportunistic theory of cellular and systems consolidation

Memories are often classified as hippocampus dependent or independent, and sleep has been found to facilitate both, but in different ways. In this Opinion, we explore the optimal neural state for cellular and systems consolidation of hippocampus-dependent memories that benefit from sleep. We suggest that these two kinds of consolidation, which are ordinarily treated separately, overlap in time and jointly benefit from a period of reduced interference (during which no new memories are formed). Conditions that result in reduced interference include slow wave sleep (SWS), NMDA receptor antagonists, benzodiazepines, alcohol and acetylcholine antagonists. We hypothesize that the consolidation of hippocampal-dependent memories might not depend on SWS per se. Instead, the brain opportunistically consolidates previously encoded memories whenever the hippocampus is not otherwise occupied by the task of encoding new memories.