The Human Medial Temporal Lobe Is Necessary for Remembering Durations within a Sequence of Events but Not Durations of Individual Events

Abstract

Recent interest in the role of the hippocampus in temporal aspects of cognition has been fueled, in part, by the observation of “time” cells in the rodent hippocampus—that is, cells that have differential firing patterns depending on how long ago an event occurred. Such cells are thought to provide an internal representation of elapsed time. Yet, the hippocampus is not needed for processing temporal duration information per se, at least on the order of seconds, as evidenced by intact duration judgments in rodents and humans with hippocampal damage. Rather, it has been proposed that the hippocampus may be essential for coding higher order aspects of temporal mnemonic processing, such as those needed to temporally organize a sequence of events that form an episode. To examine whether (1) the hippocampus uses duration information in the service of establishing temporal relations among events and (2) its role in memory for duration is unique to sequences, we tested amnesic patients with medial-temporal lobe damage (including the hippocampus). We hypothesized that medial-temporal lobe damage should impair the ability to remember sequential duration information but leave intact judgments about duration devoid of a sequential demand. We found that amnesics were impaired in making judgments about durations within a sequence but not in judging single durations. This impairment was not due to higher cognitive load associated with duration judgments about sequences. In convergence with rodent and human fMRI work, these findings shed light on how time coding in the hippocampus may contribute to temporal cognition.

The Medial Temporal Lobe Supports Mnemonic Discrimination For Event Duration

“…With respect to previous studies involving humans 594 (Aminoff et al, 2007;Clewett & Davachi, 2017;Diana et al, 2013;El-Kalliny et al, 2019;595 Hsieh et al, 2014;Jenkins & Ranganath, 2010Montchal et al, 2019;F. Wang & Diana, 596 2017), our results are similar in nature and any differences are likely due to the fact the we here 597 tested for episodic memory of temporal duration rather than temporal order or sequence, or 598 working memory for temporal duration (Palombo et al, 2019). As such, we partially reject 599 hypothesis (d), as we did find differential activation in the MTL associated with the task, but not 600 in the hypothesized region of CA1.…”

“…we reject the null of hypothesis (a), given that participants had d' scores which differed 478 significantly from zero, but fail to reject the null of hypotheses (b) and (c); participants were 479 equally sensitive at Lag 4 as at Lag 12 and were equally sensitive to increases and decreases in 480 duration. These subsecond findings replicate those of Palombo et al (2019), in which amnestic 481 patients were tasked detecting whether test spinwheels spun for a different duration than study 482 pinwheels. Palombo et al (2019) noted, as we do here, that participants had strong d' scores and 483 were sensitive to both increases and decreases in duration.…”

“…These subsecond findings replicate those of Palombo et al (2019), in which amnestic 481 patients were tasked detecting whether test spinwheels spun for a different duration than study 482 pinwheels. Palombo et al (2019) noted, as we do here, that participants had strong d' scores and 483 were sensitive to both increases and decreases in duration. Further, in the present experiment, no 484 effect of lag was detected; equal performance at either lag suggests that the distracting task was 485 sufficiently difficult to overwhelm working memory such that behavioral results here are 486 reflective of episodic memory processes.…”

“…Related work include a set of experiments conducted by Barnett et al (2014), which clearly demonstrated that human participants were capable of detecting second and sub-second changes to both inter-stimulus and event durations when presented with a series of images, a behavior which was associated with differential hippocampal activity. Also, work by Palombo et al (2019) demonstrated that medial temporal lobe patients were successful at detecting whether a set of stimuli changed in duration from that of another set. We note, though, that both experiments were operating within a time frame largely governed by working memory, and Thavabalasingam (2019) is the only study of which we are aware that tested episodic memory for temporal duration.…”

The effect of stress on memory for temporal context

“…Stress influences memory through a complex time-dependent interaction of noradrenalin and glucocorticoids with hippocampal functioning. The hippocampus is, among other functions, considered central for encoding specific temporal relationships between episodic events (Bellmund et al, 2020(Bellmund et al, , 2021Palombo et al, 2020) and binding episodic events to a temporal context (DuBrow & Davachi, 2013;Eichenbaum et al, 2007;Reeders et al, 2018). The effect of stress on memory has been studied extensively over the past few decades across multiple areas of memory research such as encoding, retrieval (Schwabe & Wolf, 2010Wolf, 2009), spatial contextualization (Sazma et al, 2019;van Ast et al, 2013), implicit memory (Meyer et al, 2013;Römer et al, 2011), and emotional memory (Joëls et al, 2011;Payne et al, 2006).…”