Memory Traces Diminished by Exercise Affect New Learning as Proactive Facilitation

Abstract

Exercise enhances cognitive function through increased neurogenesis but can also cause neurogenesis-induced forgetting. It remains unclear whether the diminished memory traces are completely forgotten. Our goals were to determine whether spatial memory is diminished by exercise, and if so, whether the memory is completely gone or whether only the local details disappear but not the acquired strategy. Two-monthold male C57BL/6J mice were trained on a spatial memory task using the Morris water maze and tested to determine that they had learned the platform location. Another mouse group received no training. Half the mice in each group then exercised on a running wheel, while the other half remained sedentary in home cages. After 4 weeks of this, previously trained mice were tested for their retention of the platform location. All mice were then subjected to the task, but the platform was located in a different position (reversal learning for previously trained mice). We found that exercise significantly facilitated the forgetting of the first platform location (i.e., diminished spatial memory) but also significantly enhanced reversal learning. Compared with mice that received no pre-exercise training, mice that had been previously trained, even those in the exercise group that had decreased recall, showed significantly better performance in the reversal learning test. Activation of new adult-born neurons was also examined. Although newborn neuron activation between groups that had or had not received prior task training was not different, activation was significantly higher in exercise groups than in sedentary groups after the probe test for reversal learning. These results indicated that the experience of pre-exercise training equally facilitated new learning in the sedentary and exercise groups, even though significantly lower memory retention was found in the exercise group, suggesting rule-based learning in mice. Furthermore, newborn neurons equally participated in similar and novel memory acquisition.

A mind in motion: Exercise improves cognitive flexibility, impulsivity and alters dopamine receptor gene expression in a Parkinsonian rat model

“…While in the current study, exercise effects on nose-poke accuracy of lesioned rats were modest during the reversal phase, greater effects were noted for premature responses, a measure of impulsivity and response inhibition. The decrease in premature responses is consistent with an improved ability of the exercised animal to acquire new learning, either because of a lower exercise-related recall of the prior rule set as previously proposed ( Epp et al, 2016 ; Li et al, 2020 ), or possibly through facilitated suppression of the prior rule-based learning. The findings of diminished premature responses mirror a report in PD patients where 6 weeks of intermittent aerobic walking elicits significant improvement in cognitive inhibition (Flanker test) but not in set shifting (Wisconsin card sort, Trail Making tests) ( Uc et al, 2014 ).…”

“…Exercise is well known to elicit broad changes in neuroplasticity, including increases in neurogenesis ( Ma et al, 2017 ). Increases in exercise-related neurogenesis have been reported to be associated with lower memory retention, while at the same time facilitating new learning, including reversal learning ( Li et al, 2020 ). It has been proposed that such improved new learning may be the result of a decrease in proactive interference which usually occurs when consolidated memories inhibit new learning ( Epp et al, 2016 ).…”

Chimera Patterns of Synchrony in a Frustrated Array of Hebb Synapses

“…This means that a neuronal circuit is involved in the recollection of a particular memory (Mayford et al, 2012 ). It is then possible to affect learning by changing the strength of the associated memory trace (Li et al, 2020 ). In our study, it is the notion of frustration that is important for memory, as we discuss in the next section.…”