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Short-Term Memory

For medical students2 min readUpdated 2026-10-10

Short-term (or working) memory is a functional information-processing stage formed on the basis of a sensory trace of the external environment. It ensures the retention and recall of a strictly selected portion of data for a period ranging from several seconds to a few minutes.

DurationRetention of traces from several seconds to a few minutes

Memory CapacityAn average of 7 ± 2 items of information in humans

MechanismReverberation (circulation) of nerve impulses in neural circuits

ConsolidationMemory traces become stable after 4 hours

VulnerabilityDisrupted by hypoxia, trauma, general anesthesia, and electroconvulsive shock

Functional Significance and Capacity

Short-term memory serves as a critical filter through which information about the surrounding world passes. It forms directly from the sensory trace received from sensory organs.

An essential feature of this type of memory is strict data selection. Not the entire array of external stimuli enters short-term memory, but only the limited volume of information highlighted by the dominant motivation. This array is necessary for the organism to satisfy its leading, most pressing need at the moment.

The capacity of human short-term memory is strictly limited to 7 ± 2 items. A classic example confirming this: if a subject is presented once with a list of meaningless words, they can reproduce them in this exact equivalent quantity. Anything exceeding this limit is displaced and not retained without additional repetition.

Neurophysiological Mechanisms

Current theories regarding how the brain holds information for a short duration are based on the hypothesis of nerve impulse circulation. The process unfolds in several stages:

Excitation originates in the primary transmitting element—the pyramidal neuron.
From the pyramidal cell, the signal spreads along its collaterals (axonal side branches).
These collaterals transmit the impulse to a specific group of interneurons—interneurons.
A local closed neural circuit is formed.
Within this circuit, reverberation of excitation begins—the repeated circulation of the same nerve impulses in a loop.

This dynamic process of reverberation is recognized as the physiological basis of short-term memory. As long as impulses "run" through the closed loop, the information remains accessible for recall.

Consolidation: The Path to Long-Term Storage

For information not to vanish completely after reverberation ceases, the process of memory consolidation must be triggered. The essence of this process is the transition of fragile short-term memory traces into a stable, fixed state.

Processes ensuring the subsequent transfer of information into intermediate and then long-term memory unfold over several hours following the completion of the short-term phase. The time factor is crucial here:

In the initial period, memory traces are highly unstable.
Final stability is achieved only after 4 hours.

Before this period elapses, any extreme exposures (both chemical and mechanical) can irreversibly erase the unconsolidated information.

Memory Impairments and Retrograde Amnesia

Due to its functional nature (impulse circulation), short-term memory is extremely sensitive to damaging factors. Its normal operation is severely disrupted by electroconvulsive shock, major brain trauma, seizures, hypoxia (oxygen deprivation), and general anesthesia.

The clinical and experimental manifestation of this failure is retrograde amnesia—complete loss of memory for events immediately preceding the extreme exposure.

Experimental data using electroconvulsive shock clearly demonstrate memory's dependence on the consolidation window:

If electroshock is applied immediately after learning, it wipes out short-term memory traces, causing profound amnesia.
If the exposure occurs several hours after the learning session (when consolidation is complete), memory is entirely unaffected.

Notably, in retrograde amnesia, only fresh, unconsolidated traces are lost. Previously acquired life experiences and information that has already transitioned into long-term memory remain completely intact.

A specialized test is used to evaluate the state of short-term memory and its impairments in laboratory settings. It involves determining the critical time interval required for a previously trained subject to perform correct instrumental actions in response to a conditional signal, especially when this signal is delayed from reinforcement.

Mnemonic

To remember the short-term memory capacity, use the "Magical Number 7 ± 2" rule—imagine your brain can simultaneously juggle 5 to 9 fact-balls. Add one more, and the whole structure collapses.

Frequently asked questions

Which brain structures play a key role in memory consolidation?

The hippocampus plays a key role in memory consolidation (the transition from short-term to long-term memory). The process also involves deep regions of the temporal lobes and the limbic system; bilateral damage to these areas disrupts information fixation.

What molecular and biochemical mechanisms underlie the transition from short-term to long-term memory?

This transition (engram consolidation) is based on the activation of the neuronal genetic apparatus and de novo protein synthesis. The process involves a cascade of reactions: stimulus convergence triggers secondary messengers, the signal reaches the nucleus, early genes are expressed, and proteins are synthesized (DNA transcription to RNA, followed by translation). Synthesized proteins alter synapse or neuron structure, ensuring long-term plasticity.

What is the methodology of the critical time interval test?

The methodology involves determining the critical time interval needed for a trained subject to perform correct instrumental actions in response to a conditioned signal when it is delayed from reinforcement.

How does retrograde amnesia differ from anterograde amnesia?

Retrograde and anterograde amnesia differ in their temporal relationship to the onset of the disease or pathological factor.

Feature	Retrograde Amnesia	Anterograde Amnesia
Nature of impairment	Loss of memories for events occurring before the disease/injury	Inability to retain new information after the injury / onset of illness
Relation to consolidation	A short period before the trauma typically drops out (events failed to consolidate)	Retention of new information is impaired

What is the physiological basis of short-term memory?

Its basis is the reverberation of excitation—the circulation of nerve impulses through closed loops formed by pyramidal neurons and their collaterals connected to interneurons.

How long does memory consolidation take?

The transition of short-term memory traces into a stable state takes time. Normally, traces become fully stable after 4 hours.

Why do only recent events get erased during a concussion?

This phenomenon is called retrograde amnesia. Physical trauma interrupts impulse reverberation and destroys short-term memory traces before they can consolidate, while older long-term memory remains intact.

How are short-term memory impairments assessed experimentally?

The critical time interval test is used. It measures the time required for a trained subject to provide a correct instrumental response to a signal delayed from reinforcement.

Go deeper

Mechanisms of sensory trace formation from the external environment
The role of dominant motivation in selecting information for memory encoding
Processes of information transfer into intermediate memory
Differences between retrograde amnesia and other memory disorders
Methods for experimental modeling of electroconvulsive shock and hypoxia