psychology Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...

, associative memory is defined as the ability to

learn Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, Attitude (psychology), attitudes, and preferences. The ability to learn is possessed by humans, non-human animals, and ...

and remember 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 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'' 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 memory, long-term human memory, the other of which is implicit memory. Explicit memory is the Consciousness, conscious, intentional Recall (memory), recollection of f ...

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 in which voluntary behaviors are modified by association with the addition (or removal) of reward or aversive stimuli. The frequency or duration of the behavior ma ...

and

classical conditioning Classical conditioning (also respondent conditioning and Pavlovian conditioning) is a behavioral procedure in which a biologically potent Stimulus (physiology), stimulus (e.g. food, a puff of air on the eye, a potential rival) is paired with a n ...

. 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 and functionally connected cortical areas. The main locations are the

hippocampus The hippocampus (: hippocampi; via Latin from Ancient Greek, Greek , 'seahorse'), also hippocampus proper, is a major component of the brain of humans and many other vertebrates. In the human brain the hippocampus, the dentate gyrus, and the ...

and its surrounding structures of the entorhinal, 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 injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

s have shown to have impairments in recognition memory 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. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...

, frontal motor areas, and the

striatum The striatum (: striata) or corpus striatum is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. The striatum is a critical component of the motor and reward systems; receives glutamat ...

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 specializing in neuroscience that deals with the anatomy and function of neurons, Biological neural network, neural circuits, and glia, and their Behavior, behavioral, biological, and psycholo ...

s for the last few decades. The convergence of the biologically important information drives the neural plasticity 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 over prefrontal cortex has improved performance on associative memory tasks, but recent studies that stimulated posterior parietal cortex showed more reliable effects. Patients with

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

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 of large

neural network A neural network is a group of interconnected units called neurons that send signals to one another. Neurons can be either biological cells or signal pathways. While individual neurons are simple, many of them together in a network can perfor ...

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