Facilitation of human long-term memory with post-learning physical exercise

Memory consolidation refers to the processes through which initially encoded
memories are transformed into a more stable enduring form. The neural and
behavioural processes that mediate consolidation, and thus ensure long-term
memory retention, are poorly understood in humans. Recent animal research has
led to the *Synaptic Tagging and Capture* hypothesis. This theory postulates
that cellular processes of memory consolidation can be divided into an early
and a late phase. In the early consolidation phase, a potential for
long-lasting neural change is created by the initial experience of the
to-be-remembered event. However, this potential is only realized as a
persistent change in the late consolidation phase when it is accompanied by
certain molecular events. Chief amongst those events is local dopaminergic and
adrenergic activation, and the release of plasticity-related proteins. In the
absence of these phenomena, initial potentiation decays within 2 hours after
initial memory encoding, and long-term memory formation is not possible.
However, it has been shown in animals that, within this critical time period,
molecular and behavioural interventions that increase dopaminergic and
adrenergic signalling can rescue memories that would have otherwise decayed.
Interestingly, physical exercise has been associated with increased
dopaminergic and B-adrenergic release as well as increased plasticity, mostly
through upregulation of BDNF and other neurotrophins. The size of these
physiological changes scales with exercise intensity. As such, current theory
would predict that performance of intense exercise within 2 hours of learning
is beneficial for long-term memory retention. In contrast, physical exercise
more than 2 hr after learning (outside the critical time period for
consolidation) is not predicted to be effective. The current exploratory study
will test these predictions in the healthy human population.

To examine the behavioural and neural effects of a single session of
post-learning exercise on long-term memory retention in humans.

Single centre, exploratory, randomized open between-subject intervention study
in parallel groups with fMRI measurements during memory retrieval.

Two experimental groups participate in high intensity physical exercise and a
control session after performing an associative memory task. Experimental
groups differ only in the order of experimental conditions performed
(control->exercise vs exercise->control) but experience both conditions over
the course of the study. Exercise consists of one sub-maximal stationary
bicycle interval training session of 35 minutes. The intensity level of the
exercise will be based on the predicted maximum heartrate of each subject, and
will therefore be adjusted on an individual-to-individual basis. The maximum
heartrate is the highest heartrate that a subject can achieve without
experiencing complications,and will be estimated using an age-corrected
formula. These calculations do not require a physical exercise test. The "high
intensity" exercise session will have a maximum intensity of 80% of the maximum
heartrate.

Sub-maximal bicycle exercise is associated with negligible safety risks in
young healthy volunteers without hypertension, normal ECG and without a history
of cardiovascular disease. MRI recordings are safe if conducted by qualified
personnel and
proper precautions are taken.