Many students have probably discovered that no amount of pedagogic ingenuity can inspire academic motivation more than the combination of 4:00 a.m. on the corner of one’s computer screen and an 8:00 a.m. alarm labeled “EXAM” on one’s phone. Accordingly, many students should also be familiar with the unsettling chill of a mental blank when asked to recall the content of such exams retrospectively. Indeed, the fact that last-minute cramming might not be very conducive to long-term memory consolidation is not just a figment of conscience, but also a neuro-scientifically corroborated phenomenon.
A brief overview of a neuron, or nerve cell, is necessary to understand memory. Unlike other cells, a neuron contains voltage-gated ion channels on its membrane that open when its receptors are bound by neurotransmitters (chemical messengers). This allows ions to enter the neuron, propagate a positive charge along the cell body, and eventually trigger the release of the neuron’s own neurotransmitters. Neurons of the same effector pathway communicate across synapses, or gaps across which neurotransmitters can diffuse from one neuron to receptors on the next, stimulating another action potential (firing of neuron) or effector cell functions.
One special neural mechanism by which long-term memory is established and strengthened is called long-term potentiation (LTP). LTP is a phenomenon in which neuron response to neurotransmitters increases in sensitivity with repeated stimulation. Most prominent in the hippocampus, LTP is driven by NMDA-type glutamate receptors. Unlike normal neuron receptors that fire upon binding of neurotransmitters, NMDA receptors are blocked by a magnesium ion and are unresponsive to weak stimulation. However, if a particular memory pathway is activated frequently, multiple stimulations can combine to trigger a strong action potential and displace the Mg2+ ion from the NMDA receptor. The receptor then activates a signal cascade to make structural changes in the neural synapse, such as the introduction of new receptors or an increase in neurotransmitter production. The higher the number of receptors or neurotransmitter production in a synapse, the more sensitive the neuron will become to stimulation. In brief, NMDA receptors increase the sensitivity and efficiency of neural communication in frequently used pathways. LTP is what causes a subject to “click,” and manifests in the improvement of one’s ability to quickly and accurately retrieve frequently used memories or skills.
While 3 a.m. coffee binges in the library may seem like an efficient blitzkrieg approach to tackling a final, it also causes one to miss out on the full benefits of the brain’s remarkable plasticity for higher efficiency, which can only be accomplished with time.
The principle of neural plasticity (the concept that synapses are susceptible to growth and atrophy to accommodate modifications in brain mapping) that drives LTP also gives rise to the spacing effect. More relevant to cramming, the spacing effect explains that it is more likely for someone to remember facts by spacing out study sessions rather than combining them. In fact, the longer the interval of separation between sessions, the more vividly the memories can be retained. At a cellular level, neurons can reorganize networks and grow new synapses at potentially useful locations during the long time interval between two rehearsal sessions. Thus, subsequent rehearsal can more effectively increase the efficiency of neural connections and reduce retrieval noise. Just like LTP, the spacing effect elevates the sensitivity of particular neural pathways and improves memory retention and retrieval. In contrast, a single prolonged training session can increase memory connectivity only slightly above regular anatomical connectivity. While 3 a.m. coffee binges in the library may seem like an efficient blitzkrieg approach to tackling a final, they also cause one to miss out on the full benefits of the brain’s remarkable plasticity for higher efficiency, which can only be accomplished with time. Hence, just like intuition might predict, cramming is not the most efficient strategy after all.
 Byrne, “Learning and Memory.”
 Knoblauch, “Structural Plasticity, Cortical Memory, and the Spacing Effect.”