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

Abstract

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.

Refresh my memory: Episodic memory reinstatements intrude on working memory maintenance

“…This distribution of substitutions is consistent with previous observations that, when working memory maintenance is interrupted, participants use episodic memory to maintain information over short delays (Lewis-Peacock et al, 2016;Zanto et al, 2016;Rose et al, 2014). Our results establish that the context-based nature of errors can serve as a signature of episodic memory use in a short-term retention task, especially when retention in working memory is subject to interference.…”

“…In the second phase, participants performed a short-term delayed-recall task in which (on each trial) they saw a set of four target words that they needed to recall after an 18-second delay; we manipulated whether the delay was unfilled (no distraction), or participants did 6 seconds of backwards counting at the outset of the delay (break distraction, as in: we were briefly "breaking up" their ability to maintain information in working memory), or participants counted backwards throughout the full 18-second delay (full distraction). Previous studies using this kind of short-term recall test have found that distraction during the delay causes participants to rely on episodic rather than working memory, as evidenced by the fact that errors are primarily words substituted from recent trials (Brown, 1958;Peterson & Peterson, 1959;Rose et al, 2014;Lewis-Peacock et al, 2016;Zanto et al, 2016). Here, we tested whether these substitutions can be biased by the encoding context of the target words.…”

Short-term memory for spatial, sequential and duration information

“…Patients with impaired medial temporal lobe pathology, specifically involving the hippocampi, were severely impaired at scene discrimination when a significant demand was placed on short term retention of complex spatial information in viewpoint independent representations [ 23 , 24 ]. Moreover, multivoxel pattern analysis of human functional imaging data supports the view that the hippocampus plays a role in binding object and location information even over short intervals [ 25 ], especially when the memory task is difficult [ 26 ]. Identity and location information was observed in the patterns of activity of perirhinal and parahippocampal cortex respectively, whereas activity patterns in the right anterior hippocampus across encoding and delay periods was predictive of accurate short-term memory for object–location relationships [ 25 ].…”

Variation in strategy use across measures of verbal working memory

“…With such a widely utilized, yet diverse, collection of WM tasks, an obvious question arises: How similar are these tasks to one another with respect to the mental processes, and strategies, that they evoke? While traditional behavioral research (Cowan, 2001; Luck & Vogel, 2013), psychometric studies (Engle, Tuholski, Laughlin, & Conway, 1999; Kane et al, 2004), and cognitive neuroimaging investigations (Nee et al, 2013; Wager & Smith, 2003) all provide some evidence that distinct WM tasks do draw upon shared processes, they also provide evidence that these tasks can operate quite differently from one another with respect to the behavioral phenomena they elicit (Morrison, Conway, & Chein, 2014; Oberauer, 2003; Ricker & Cowan, 2014), the variance they account for across individuals (Unsworth, Fukuda, Awh, & Vogel, 2014), and the specific brain circuitry that they activate (Chein, Moore, & Conway, 2011; Henson, Shallice, Gorno-Tempini, & Dolan, 2002; Zanto, Clapp, Rubens, Karlsson, & Gazzaley, 2016). …”