psychology Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries betwe ...

, associative memory is defined as the ability to

learn Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of learn ...

and

remember Remember may refer to: Film and television * ''Remember?'', a 1939 film starring Robert Taylor and Greer Garson * ''Remember'' (1926 film), an American silent drama film * ''Remember'' (2015 film), a Canadian film by Atom Egoyan, starring Chris ...

the relationship between unrelated items. This would include, for example, remembering the name of someone or the aroma of a particular perfume. This type of memory deals specifically with the relationship between these different objects or concepts. A normal associative memory task involves testing participants on their

recall Recall may refer to: * Recall (bugle call), a signal to stop * Recall (information retrieval), a statistical measure * ''ReCALL'' (journal), an academic journal about computer-assisted language learning * Recall (memory) * ''Recall'' (Overwatch ...

of pairs of unrelated items, such as face-name pairs.Matzen, Laura E., Michael C. Trumbo, Ryan C. Leach, and Eric D. Leshikar. "Effects of Non-invasive Brain Stimulation on Associative Memory". ''

Brain Research ''Brain Research'' is a peer-reviewed scientific journal focusing on several aspects of neuroscience. It publishes research reports and " minireviews". The editor-in-chief is Matthew J. LaVoie (University of Florida). Until 2011, full reviews were ...

'' 1624 (2015): 286-296. Associative memory is a

declarative memory Explicit memory (or declarative memory) is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and con ...

structure and episodically based.

Conditioning

Two important processes for learning associations, and thus forming associative memories, are

operant conditioning Operant conditioning, also called instrumental conditioning, is a learning process where behaviors are modified through the association of stimuli with reinforcement or punishment. In it, operants—behaviors that affect one's environment—are c ...

and

classical conditioning Classical conditioning (also known as Pavlovian or respondent conditioning) is a behavioral procedure in which a biologically potent stimulus (e.g. food) is paired with a previously neutral stimulus (e.g. a triangle). It also refers to the learni ...

. Operant conditioning refers to a type of learning where behavior is controlled by environmental factors that influence the behavior of the subject in subsequent instances of the stimuli. In contrast, classical conditioning is when a response is conditioned to an unrelated stimulus.

Location and circuitry

The neuroanatomical structures that govern associative memory are found in the

medial temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pro ...

and functionally connected cortical areas. The main locations are the

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...

and its surrounding structures of the

entorhinal The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in the ...

, perirhinal, and parahippocampal cortices. More recently, the parietal-hippocampal network has been identified as a key circuit for associative memory Humans with large medial temporal lobe

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

s have shown to have impairments in

recognition memory Recognition memory, a subcategory of declarative memory, is the ability to recognize previously encountered events, objects, or people.Medina, J. J. (2008)The biology of recognition memory. ''Psychiatric Times''. When the previously experienced eve ...

for different types of stimuli. The hippocampus has also shown to be the main location for

memory consolidation Memory consolidation is a category of processes that stabilize a memory trace after its initial acquisition. A memory trace is a change in the nervous system caused by memorizing something. Consolidation is distinguished into two specific processe ...

, especially related to

episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...

. The inputs from these unrelated stimuli are collected in this location and the actual synaptic connections are made and strengthened. Additionally, involvement from the

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...

, frontal motor areas, and the

striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamate ...

has been shown in the formation of associative memories. Associative memory is not considered to be localized to a single circuit, with different types of subsets of associative memory utilizing different circuitry.

Biological basis

The associations made during the learning process have a biological basis that has been studied by

neuroscientist A neuroscientist (or neurobiologist) is a scientist who has specialised knowledge in neuroscience, a branch of biology that deals with the physiology, biochemistry, psychology, anatomy and molecular biology of neurons, Biological neural network, n ...

s for the last few decades. The convergence of the biologically important information drives the

neural plasticity Neuroplasticity, also known as neural plasticity, or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganization. It is when the brain is rewired to function in some way that differs from how it ...

that is the basis of associative memory formation.

Research and future work

Associative memory becomes poorer in humans as they age. Additionally, it has been shown to be non-correlational with a single item (non-associative) memory function. Non-invasive brain stimulation techniques have emerged as promising tools for the improvement of associative memory.

Transcranial direct-current stimulation Transcranial direct current stimulation (tDCS) is a form of neuromodulation that uses constant, low direct current delivered via electrodes on the head. It was originally developed to help patients with brain injuries or neuropsychiatric conditio ...

over prefrontal cortex has improved performance on associative memory tasks, but recent studies that stimulated posterior

parietal cortex The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...

showed more reliable effects. Patients with

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

have been shown to be poorer in multiple forms of associative memory.

Mathematical models

Starting from Hopfield’s work, mathematical modeling of memory formation and retrieval has been in the center of attention. For a long time, the ability to establish the relationship between unrelated items has been considered as an emergent feature of the

nonlinear dynamics In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...

of large

neural network A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...

s. More recent experimental discovery of the so-called concept or grandmother cells ascribes some functions in episodic memory to single neurons.Quian Quiroga R
Concept cells: the building blocks of declarative memory functions.
Nat Rev Neurosci 13, 587 (2012). Mathematical modeling of grandmother cells confirms that single neurons can indeed implement associative memory. The associative property emerges in large assemblies of single neurons receiving a multidimensional synaptic input from afferent populations and synaptic plasticity obey the Hebbian rule.

References