Medial temporal lobe amnesia impairs performance on a free association task

Abstract

A growing body of evidence suggests that the hippocampus contributes to performance (or is implicated) in non-memory domains from perception to problem solving. In a previous study we found that hippocampal contribution to exemplar generation in a fluency task was determined jointly by the open-endedness of the task and its ability to elicit episodic memories (Sheldon and Moscovitch (2012) Hippocampus 22:1451-1466). In the current study, we extend these observations by exploring the role of the hippocampus in generative, goal-directed open-ended thought in patients with medial temporal lobe (MTL) amnesia on a free association task (think of words as they come to mind). Patients and control participants were asked to associate freely for one minute to cue words that varied in the open-endedness of the responses they elicited (greater for low- than high-frequency words), and in the ease with which episodic memories were evoked (greater for high imageable than low imageable words). As predicted, MTL amnesia patients generated fewer words than control participants when cues were highly imageable and low in frequency, but performed equivalently to them in the other conditions. These results support our prediction that the hippocampus contributes to free association, and possibly more generally to other generative tasks that are open-ended, creative, or that elicit the use of contextual and likely episodic memories in order to derive relevant information.

Impaired assessment of cumulative lifetime familiarity for object concepts after left anterior temporal-lobe resection that includes perirhinal cortex but spares the hippocampus

“…This possibility deserves consideration in light of prior evidence that implicates hippocampal functioning in ostensibly semantic tasks, such as object naming or conceptual fluency, i.e., the speeded generation of exemplars from different semantic categories (Klooster & Duff, 2015;Greenberg, Keane, Ryan, & Verfaille, 2009;Ryan, Cox, Hayes, & Nadel, 2008;Sheldon & Moscovitch, 2013;Westmacott & Moscovitch, 2003;Whatmough & Chertkow, 2007). Building on the widely held view that the hippocampus plays a critical role in binding items to episodic contexts (Cohen & Eichenbaum, 1993), such evidence has led to the suggestion that episodic and semantic memory may interact even on tasks that do not require any recollection, and that recollection of a pertinent autobiographical episode can help generate or retrieve semantic information (see Sheldon & Moscovitch, 2012, for detailed discussion).…”

Specific, personally meaningful cues can benefit episodic prospection in medial temporal lobe amnesia

“…Tasking MTL amnesic individuals with generating detailed episodes from non-descript everyday nouns puts them at a particular disadvantage given that hippocampal damage impairs a host of related abilities including representational generation (Duff, Kurczek, Rubin, Cohen, & Tranel, 2013), generative free association (Sheldon, Romero, & Moscovitch, 2013), detail generation and binding (Rosenbaum et al, 2009), and open-ended problem-solving (Sheldon, McAndrews, & Moscovitch, 2011). Impairment in these related processes bypasses the divergent thinking involved in creating a detailed episode from a single word.…”

Ill-defined problem solving in amnestic mild cognitive impairment: Linking episodic memory to effective solution generation

“…Consistent with our proposal, another possibility is that the hippocampus helps create a "memory space" where scenarios of possible outcomes can be simulated via flexible association amongst never-before experienced items (Eichenbaum et al, 1999) or updating older representations with newly experienced information. The latter may help explain why a variety of tasks that require flexible associative thought but not traditional memory processes (e.g., creativity, inferential reasoning, decisionmaking and problem-solving) implicate the hippocampal system (Gupta et al, 2009;Gutbrod et al, 2006;Sheldon et al, 2013;Zeithamova et al, 2012).…”