State-dependent memory
State-dependent memory or state-dependent learning is the phenomenon where people remember more information if their physical or mental state is the same at time of encoding and time of recall. State-dependent memory is heavily researched in regards to its employment both in regards to synthetic states of consciousness as well as organic states of consciousness such as mood. While state-dependent memory may seem rather similar to context-dependent memory, context-dependent memory involves an individual's external environment and conditions while state-dependent memory applies to the individual's internal conditions.
History of research
In 1784, a French aristocrat named Marquis de Puységur, realized that when people were put in a hypnotic state then awoken, they had no recollection of what they were told. However, when they were put back under hypnosis, in the state they would be able to recall everything from the last time.In 1910, a man named Morton Prince came to a realization about dreams. He hypothesized that the reason we have a hard time remembering our dreams when we wake up is not due to the fact that we are unable to, but because dreams are not like the real world.
In 1937, at the University of Illinois, Edward Girden and Elmer Culler conducted an experiment on conditioned responses in dogs under the influence of the drug curare. In the experiment, dogs were taught a conditioned muscular response – to draw their paw away from the ground when they heard a buzzer. The buzzer was often accompanied by a small electric shock, which motivated the response. For dogs that had been under the influence of curare when they first learned the response, after the curare was no longer in their system, they were less likely to remember to draw their paw away on hearing the buzzer. Once they were given curare again, the response returned. This result indicated that the dogs' ability to recall the responses was connected to their state of consciousness. Girden and Culler's research opened the door for further investigation of the influences of state of consciousness on an organism's ability to encode memory.
Following this discovery, other researchers looked into the effect of different states of being on the ability to learn and remember responses or information. In 1964, Donald Overton conducted a study as a direct response to Girden and Culler's 1937 experiment. The study tested the effects of sodium pentobarbital on rats' abilities to learn and remember certain taught responses. These rats were randomly assigned to one of two groups – substance administered or no substance administered – and then placed in a simple maze and taught to escape an electrical shock. Overton found that the rats that had been administered 25 mg of sodium pentobarbital could no longer remember the proper escape response when they were later placed in the maze without the drug. However, if these rats were administered sodium pentobarbital once again and placed in the maze, they recalled the escape response they had been taught. Similarly, when Overton taught a rat the escape response under the control condition, it could not recall that behavior when it was administered the drug and asked to perform later on. Results strongly indicated that rats performed the learned response more efficiently when in the either sodium pentobarbital or control state that they were in when they first learned it. In regard to this idea the study specifically stated "a response learned under the influence of a particular drug will subsequently reoccur only when that drug condition is reinstated".
In 1969, Hoine, Bremer, and Stern conducted a test with two main parts. The participants were given time to study and just before they were tested they were asked to consume 10 ounces of Vodka. The very next day they did the same thing except some were intoxicated, while others remained sober. The results found that whether the students were sober or intoxicated they did well, but only if the state they were in was the same when they studied and when they were tested. In other words if they were intoxicated while they studied, then they did better taking the test in the same state. If they were sober when they studied then they got their best results while sober.
In later years, similar studies confirmed that learning could be state-dependent. In 1971, Terry Devietti and Raymond Larson conducted a similar study in rats, seeing how memory was affected by various levels of electric shock. Their results supported the idea that the rats' ability to remember a learned response was influenced by their state. The phenomenon continued to be studied more than thirty years later. In 2004, Mohammad-Reza Zarrindast and Ameneh Rezayof studied mice, to see
how memory and learning were affected by morphine. They found that when mice learned a response under the influence of morphine, they later performed it most efficiently under the influence of morphine. When mice learned the response free of morphine, they recalled it best when similarly sober. And for mice that were taught the response under the
influence of morphine, once the drug wore off, they suffered amnestic effects; they could no longer remember the learned response.
The results of each of these studies points to the existence of a state-dependent memory phenomenon. Further research on the subject continues to be carried out today in order to discover further implications of state-dependent memory or other situations in which state-dependent memory might take place.
In 1979, Reus, Post, and Weingartner, found that when a person is depressed they find it nearly impossible to think of a time in the past when they were happy. The longer they were depressed the more impossible the task became. They attributed this to the mind taking control of how the person felt. The person feels nothing but misery so, therefore, that is what their whole life must have been like both before and after the depression to hold.
In 1999 a psychiatry journal was published on the topic of spouse abuse. The main topic of discussion was about men who would abuse their wives, sometimes even killing them and having no memory of the event afterward. At first they were just thought to be lies but with later findings they found that many convicts have said the same thing. They remember the time before the attack and after, but have no memory of the attack itself. One man described it as everything going red as though he had blacked out. In this journal it is discussed that state-dependent memory might be to blame. The thought process behind this theory is that the individuals experience what is known as limited amnesia. This form of amnesia is specific towards one event that has been forgotten. The idea is that the person got so mad/angry at their spouse that they cannot recall what they did because it is so out of character for them. This could be attributed to the person choosing not to remember and losing the memory or due to the alcohol that is usually consumed.
In 2019 a study of 100 college-aged women between the age of 18–24 were given questionnaires daily to access how alcohol had an effect on their memories of a past sexual assault. Some of the women were intoxicated during the assault and about half were not. Women who were intoxicated during the assaults would experience intrusive thoughts and flashbacks of the SA. Whereas, women who were not intoxicated at the time of their assault experienced no more flashbacks or intrusive thoughts than usual. It is common for alcohol to be attributed to forgetting, but when encoding happens specifically while under the influence of alcohol it can make the memory more vivid.
Biological functions and explanatory mechanisms
At its most basic, state-dependent memory is the product of the strengthening of a particular synaptic pathway in the brain. A neural synapse is the space between brain cells, or neurons, that allows chemical signals to be passed from one neuron to another. Chemicals called neurotransmitters leave one cell, travel across the synapse, and are taken in by the next neuron through a neurotransmitter receptor. This creates a connection between the two neurons called a neural pathway. Memory relies on the strengthening of these neural pathways, associating one neuron with another. When we learn something, new pathways are made between neurons in the brain which then communicate through chemical signals. If these cells have a history of sending out certain signals under specific chemical conditions within the brain, they are then primed to work most effectively under similar circumstances. State-dependent memory happens when a new neural connection is made while the brain is in a specific chemical state – for instance, a child with ADHD learns their multiplication tables while on stimulant medication. Because their brain created these new connections related to multiplication tables while the brain was chemically affected by the stimulant medication, their neurons will be primed in the future to remember these facts best when the same levels of medication are present in the brain.While there is strong evidence for the existence of state-dependent memory, it is less clear what the advantage of this circumstance might be. In 2006, researcher Lorena Pomplio and her team tackled this question as they investigated the presence of state-dependent memory in invertebrates, specifically grasshoppers. Up until this point, only vertebrates had been used to study state-dependent memory. This study found that invertebrates did indeed experience the phenomenon as well, particularly in regard to conditions of low or high nutritional intake. Pomplio and associates concluded that their results demonstrated a potential "adaptive advantage" of state-dependent learning that explains its intrinsic presence in such a wide variety of species. State-dependent memory recalls a time that the organism was in a similar condition, which then informs the decisions they make in the present. For these grasshoppers, their low nutritional state sparked cognitive connections to similar states of duress and primed the insects to make decisions they had made when faced with low nutrition in previous conditions. The paper suggests that this phenomenon allows for quick decisions to be made when an organism does not have the time or neural capability to carefully process every option.