Lifespan developmental invariance in memory consolidation: evidence from procedural memory

Abstract

Characterizing ontogenetic changes across the lifespan is a crucial tool in understanding neurocognitive functions. While age-related changes in learning and memory functions have been extensively characterized in the past decades, the lifespan trajectory of memory consolidation, a critical function that supports the stabilization and long-term retention of memories, is still poorly understood. Here we focus on this fundamental cognitive function and probe the consolidation of procedural memories that underlie cognitive, motor, and social skills and automatic behaviors. We used a lifespan approach: 255 participants aged between 7 and 76 years performed a well-established procedural memory task in the same experimental design across the whole sample. This task enabled us to disentangle two critical processes in the procedural domain: statistical learning and general skill learning. The former is the ability to extract and learn predictable patterns of the environment, while the latter captures a general speed-up as learning progresses due to improved visuomotor coordination and other cognitive processes, independent of acquisition of the predictable patterns. To measure the consolidation of statistical and general skill knowledge, the task was administered in two sessions with a 24-h delay between them. Here, we report successful retention of statistical knowledge with no differences across age groups. For general skill knowledge, offline improvement was observed over the delay period, and the degree of this improvement was also comparable across the age groups. Overall, our findings reveal age invariance in these two key aspects of procedural memory consolidation across the human lifespan.

Keywords: consolidation; lifespan approach; procedural memory; statistical learning.

Fig. 1.

The Alternating Serial Reaction Time (ASRT) task. (A) Pattern and random trials were presented in an alternating fashion; the trial types were indistinguishable on the surface level: a picture of a dog's head served as stimuli in all trials. The alternating sequence was coded by the location of stimuli. In pattern trials, the location of stimuli was predetermined, and occurred in the same order throughout the experiment. In random trials, randomly chosen locations out of the four possible ones were presented. (B) An example of the sequence structure. Numbers indicate the predetermined stimulus locations in pattern trials, and rs indicate randomly selected locations out of the four possible ones. Due to the alternating sequence, some runs of three consecutive trials (triplets) were more probable than others, referred to as high-probability (green shading) and low-probability triplets (blue shading), respectively. Since high-probability triplets could occur as pattern-ending triplets (50% of all trials) and by chance as random-ending triplets (12.5% of all trials), these triplets constituted 62.5% of all trials. Low-probability triplets constituted the remaining 37.5% of the trials; these were all random-ending triplets. Note that triplets were identified using a moving window throughout the stimulus stream: each trial was categorized as the third element of a high- or a low-probability triplet; the same trial then served as the middle and the first element for the categorization of the following triplets. (C) Experimental procedure. The experiment consisted of two sessions. The Learning Phase was composed of four epochs (each epoch contained five blocks with 85 trials in each block). The Testing Phase consisting of one epoch was administered 24-h later. Figs. 1A and 1B are adapted from Nemeth et al. (27) and Zavecz et al. (52), and Fig. 1C is adapted from Kóbor et al. (41).

Fig. 2.

Consolidation of statistical knowledge over the 24-h offline period across age groups. RT statistical learning scores for the last epoch of the Learning Phase (Epoch 4, light gray bars) were contrasted with those for the first epoch of the Testing Phase (Epoch 5, dark gray bars). BF₀₁ values were obtained by paired-samples t-tests for this contrast separately for each age group. All reported BF₀₁ values indicate substantial evidence for the null-hypothesis (BF₀₁ > 3), providing evidence for comparable knowledge in Epoch 4 and Epoch 5 in each age group. Error bars denote the standard error of mean.

Fig. 3.

Consolidation of general skill knowledge over the 24-h offline period across age groups. Average RT values for the last epoch of the Learning Phase (Epoch 4, light gray bars) were contrasted with those for the first epoch of the Testing Phase (Epoch 5, dark gray bars). BF₀₁ values were obtained by paired-samples t-tests for this contrast separately for each age group. BF₀₁ values for all age groups except for the 61- to 76-year olds indicate substantial evidence for the alternative hypothesis (BF₀₁ < 0.33) providing evidence for offline learning over the 24-h delay. BF₀₁ value obtained for the 61- to 76-year olds could not provide evidence for either the null or the alternative hypotheses. Error bars denote the standard error of mean.