Associative memory (psychology)

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In psychology, associative memory is defined as the ability to learn and remember the relationship between unrelated items. This would include, for example, remembering the name of someone or the aroma of a particular perfume. [1] 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. [2] Associative memory is a declarative memory structure and episodically based. [3]

Contents

Conditioning

Two important processes for learning associations, and thus forming associative memories, are operant conditioning and classical conditioning. 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 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 [4] Humans with large medial temporal lobe lesions have shown to have impairments in recognition memory for different types of stimuli. [5] The hippocampus has also shown to be the main location for memory consolidation, especially related to episodic memory. The inputs from these unrelated stimuli are collected in this location and the actual synaptic connections are made and strengthened. [6] Additionally, involvement from the prefrontal cortex, [7] [8] frontal motor areas, [9] and the striatum 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. [7]

Biological basis

The associations made during the learning process have a biological basis that has been studied by neuroscientists for the last few decades. The convergence of the biologically important information drives the neural plasticity that is the basis of associative memory formation. [7]

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. [10] 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, [2] but recent studies that stimulated posterior parietal cortex showed more reliable effects. [11] [12] Patients with Alzheimer's disease have been shown to be poorer in multiple forms of associative memory. [13]

Mathematical models

Starting from Hopfield’s work, [14] 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 networks. [15] More recent experimental discovery of the so-called concept or grandmother cells ascribes some functions in episodic memory to single neurons. [16] Mathematical modeling of grandmother cells confirms that single neurons can indeed implement associative memory. [17] 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.

See also

Related Research Articles

<span class="mw-page-title-main">Entorhinal cortex</span> Area of the temporal lobe of the brain

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. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning; the association of impulses from the eye and the ear occurs in the entorhinal cortex.

Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to sensory memory, the initial stage, and short-term or working memory, the second stage, which persists for about 18 to 30 seconds. LTM is grouped into two categories known as explicit memory and implicit memory. Explicit memory is broken down into episodic and semantic memory, while implicit memory includes procedural memory and emotional conditioning.

<span class="mw-page-title-main">Long-term potentiation</span> Persistent strengthening of synapses based on recent patterns of activity

In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons. The opposite of LTP is long-term depression, which produces a long-lasting decrease in synaptic strength.

Hebbian theory is a neuropsychological theory claiming that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell. It is an attempt to explain synaptic plasticity, the adaptation of brain neurons during the learning process. It was introduced by Donald Hebb in his 1949 book The Organization of Behavior. The theory is also called Hebb's rule, Hebb's postulate, and cell assembly theory. Hebb states it as follows:

Let us assume that the persistence or repetition of a reverberatory activity tends to induce lasting cellular changes that add to its stability. ... When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased.

<span class="mw-page-title-main">Olfactory bulb</span> Neural structure

The olfactory bulb is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning.

<span class="mw-page-title-main">Temporal lobe</span> One of the four lobes of the mammalian brain

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.

<span class="mw-page-title-main">Fear conditioning</span> Behavioral paradigm in which organisms learn to predict aversive events

Pavlovian fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events. It is a form of learning in which an aversive stimulus is associated with a particular neutral context or neutral stimulus, resulting in the expression of fear responses to the originally neutral stimulus or context. This can be done by pairing the neutral stimulus with an aversive stimulus. Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of classical conditioning, the neutral stimulus or context is the "conditional stimulus" (CS), the aversive stimulus is the "unconditional stimulus" (US), and the fear is the "conditional response" (CR).

Spike-timing-dependent plasticity (STDP) is a biological process that adjusts the strength of connections between neurons in the brain. The process adjusts the connection strengths based on the relative timing of a particular neuron's output and input action potentials. The STDP process partially explains the activity-dependent development of nervous systems, especially with regard to long-term potentiation and long-term depression.

Explicit 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 concepts. This type of memory is dependent upon three processes: acquisition, consolidation, and retrieval.

Theta waves generate the theta rhythm, a neural oscillation in the brain that underlies various aspects of cognition and behavior, including learning, memory, and spatial navigation in many animals. It can be recorded using various electrophysiological methods, such as electroencephalogram (EEG), recorded either from inside the brain or from electrodes attached to the scalp.

Neural coding is a neuroscience field concerned with characterising the hypothetical relationship between the stimulus and the neuronal responses, and the relationship among the electrical activities of the neurons in the ensemble. Based on the theory that sensory and other information is represented in the brain by networks of neurons, it is believed that neurons can encode both digital and analog information.

<span class="mw-page-title-main">Reward system</span> Group of neural structures responsible for motivation and desire

The reward system is a group of neural structures responsible for incentive salience, associative learning, and positively-valenced emotions, particularly ones involving pleasure as a core component. Reward is the attractive and motivational property of a stimulus that induces appetitive behavior, also known as approach behavior, and consummatory behavior. A rewarding stimulus has been described as "any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward". In operant conditioning, rewarding stimuli function as positive reinforcers; however, the converse statement also holds true: positive reinforcers are rewarding. The reward system motivates animals to approach stimuli or engage in behaviour that increases fitness. Survival for most animal species depends upon maximizing contact with beneficial stimuli and minimizing contact with harmful stimuli. Reward cognition serves to increase the likelihood of survival and reproduction by causing associative learning, eliciting approach and consummatory behavior, and triggering positively-valenced emotions. Thus, reward is a mechanism that evolved to help increase the adaptive fitness of animals. In drug addiction, certain substances over-activate the reward circuit, leading to compulsive substance-seeking behavior resulting from synaptic plasticity in the circuit.

<span class="mw-page-title-main">Synaptic gating</span>

Synaptic gating is the ability of neural circuits to gate inputs by either suppressing or facilitating specific synaptic activity. Selective inhibition of certain synapses has been studied thoroughly, and recent studies have supported the existence of permissively gated synaptic transmission. In general, synaptic gating involves a mechanism of central control over neuronal output. It includes a sort of gatekeeper neuron, which has the ability to influence transmission of information to selected targets independently of the parts of the synapse upon which it exerts its action.

Activity-dependent plasticity is a form of functional and structural neuroplasticity that arises from the use of cognitive functions and personal experience. Hence, it is the biological basis for learning and the formation of new memories. Activity-dependent plasticity is a form of neuroplasticity that arises from intrinsic or endogenous activity, as opposed to forms of neuroplasticity that arise from extrinsic or exogenous factors, such as electrical brain stimulation- or drug-induced neuroplasticity. The brain's ability to remodel itself forms the basis of the brain's capacity to retain memories, improve motor function, and enhance comprehension and speech amongst other things. It is this trait to retain and form memories that is associated with neural plasticity and therefore many of the functions individuals perform on a daily basis. This plasticity occurs as a result of changes in gene expression which are triggered by signaling cascades that are activated by various signaling molecules during increased neuronal activity.

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 processes. The first, synaptic consolidation, which is thought to correspond to late-phase long-term potentiation, occurs on a small scale in the synaptic connections and neural circuits within the first few hours after learning. The second process is systems consolidation, occurring on a much larger scale in the brain, rendering hippocampus-dependent memories independent of the hippocampus over a period of weeks to years. Recently, a third process has become the focus of research, reconsolidation, in which previously consolidated memories can be made labile again through reactivation of the memory trace.

The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.

Recognition memory, a subcategory of explicit memory, is the ability to recognize previously encountered events, objects, or people. When the previously experienced event is reexperienced, this environmental content is matched to stored memory representations, eliciting matching signals. As first established by psychology experiments in the 1970s, recognition memory for pictures is quite remarkable: humans can remember thousands of images at high accuracy after seeing each only once and only for a few seconds.

<span class="mw-page-title-main">Nonsynaptic plasticity</span> Form of neuroplasticity

Nonsynaptic plasticity is a form of neuroplasticity that involves modification of ion channel function in the axon, dendrites, and cell body that results in specific changes in the integration of excitatory postsynaptic potentials and inhibitory postsynaptic potentials. Nonsynaptic plasticity is a modification of the intrinsic excitability of the neuron. It interacts with synaptic plasticity, but it is considered a separate entity from synaptic plasticity. Intrinsic modification of the electrical properties of neurons plays a role in many aspects of plasticity from homeostatic plasticity to learning and memory itself. Nonsynaptic plasticity affects synaptic integration, subthreshold propagation, spike generation, and other fundamental mechanisms of neurons at the cellular level. These individual neuronal alterations can result in changes in higher brain function, especially learning and memory. However, as an emerging field in neuroscience, much of the knowledge about nonsynaptic plasticity is uncertain and still requires further investigation to better define its role in brain function and behavior.

<span class="mw-page-title-main">Sleep and memory</span> Relationship between sleep and memory

The relationship between sleep and memory has been studied since at least the early 19th century. Memory, the cognitive process of storing and retrieving past experiences, learning and recognition, is a product of brain plasticity, the structural changes within synapses that create associations between stimuli. Stimuli are encoded within milliseconds; however, the long-term maintenance of memories can take additional minutes, days, or even years to fully consolidate and become a stable memory that is accessible. Therefore, the formation of a specific memory occurs rapidly, but the evolution of a memory is often an ongoing process.

<span class="mw-page-title-main">Memory</span> Faculty of mind to store and retrieve data

Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, it would be impossible for language, relationships, or personal identity to develop. Memory loss is usually described as forgetfulness or amnesia.

References

  1. ↑ Suzuki, Wendy A. (February 2005). "Associative Learning and the Hippocampus". Psychological Science Agenda. American Psychological Association.
  2. 1 2 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.
  3. ↑ Dennis, Nancy A., Indira C. Turney, Christina E. Webb, and Amy A. Overman. "The Effects of Item Familiarity on the Neural Correlates of Successful Associative Memory Encoding". Cognitive, Affective, & Behavioral Neuroscience 15.4 (2015): 889-900.
  4. ↑ Wagner AD, Shannon BJ, Kahn I, Buckner RL. "Parietal lobe contributions to episodic memory retrieval". Trends in Cognitive Sciences 9.9 (2005): 445-53.
  5. ↑ Ranganath, Charan, and Maureen Ritchey. "Two Cortical Systems for Memory-guided Behaviour". Nature Reviews Neuroscience 13.10 (2012): 713-26.
  6. ↑ Cohen, Neal J., Jennifer Ryan, Caroline Hunt, Lorene Romine, Tracey Wszalek, and Courtney Nash. "Hippocampal System and Declarative (relational) Memory: Summarizing the Data from Functional Neuroimaging Studies". Hippocampus 9.1 (1999): 83-98.
  7. 1 2 3 Fanselow, Michael S.; Poulos, Andrew M (2004-08-30). "The Neuroscience of Mammalian Associative Learning". Annual Review of Psychology . 56 (1): 207–234. doi:10.1146/annurev.psych.56.091103.070213. ISSN   0066-4308. PMID   15709934.
  8. ↑ Becker, Nina, Erika J. Laukka, Grégoria Kalpouzos, Moshe Naveh-Benjamin, Lars Bäckman, and Yvonne Brehmer. "Structural Brain Correlates of Associative Memory in Older Adults". NeuroImage 118 (2015): 146-53.
  9. ↑ Brasted P. J., Bussey TJ, Murray EA, Wise SP (2002). "Fornix transection impairs conditional visuomotor learning in tasks involving nonspatially differentiated responses". Journal of Neurophysiology 87: 631-633.
  10. ↑ Becker, Nina, Erika J. Laukka, Grégoria Kalpouzos, Moshe Naveh-Benjamin, Lars Bäckman, and Yvonne Brehmer. "Structural Brain Correlates of Associative Memory in Older Adults". NeuroImage 118 (2015): 146-153.
  11. ↑ Bjekić, J., Vulić, K., Živanović, M., Vujičić, J., Ljubisavljević, M., & Filipović, S. R. "The immediate and delayed effects of single tDCS session over posterior parietal cortex on face-word associative memory. Behavioural brain research, 2019 366: 88-95."
  12. ↑ Bjekić, J., Čolić, M. V., Živanović, M., Milanović, S. D., & Filipović, S. R. "Transcranial direct current stimulation (tDCS) over parietal cortex improves associative memory."Neurobiology of Learning and Memory, 2019, 157: 114-120.
  13. ↑ Bastin, Christine, Mohamed Ali Bahri, Frédéric Miévis, Christian Lemaire, Fabienne Collette, Sarah Genon, Jessica Simon, Bénédicte Guillaume, Rachel A. Diana, Andrew P. Yonelinas, and Eric Salmon. "Associative Memory and Its Cerebral Correlates in Alzheimer's Disease: Evidence for Distinct Deficits of Relational and Conjunctive Memory". Neuropsychologia 63 (2014): 99-106.
  14. ↑ Hopfield J.J. Neural networks and physical systems with emergent collective computational abilities. Proc Natl Acad Sci USA 79, 2554-2558 (1982)
  15. ↑ Gurney K. An introduction to neural networks, Taylor & Francis, London, New York, 2014.
  16. ↑ Quian Quiroga R. Concept cells: the building blocks of declarative memory functions. Nat Rev Neurosci 13, 587 (2012).
  17. ↑ Gorban, Alexander N.; Makarov, Valeri A.; Tyukin, Ivan Y. (July 2019). "The unreasonable effectiveness of small neural ensembles in high-dimensional brain". Physics of Life Reviews. 29: 55–88. arXiv: 1809.07656 . Bibcode:2019PhLRv..29...55G. doi: 10.1016/j.plrev.2018.09.005 . PMID   30366739.
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