Effect of caffeine on memory
is a bitter, white crystalline xanthine alkaloid that acts as a psychoactive stimulant drug. It can have both positive and negative effects on different aspects of memory.
Short-term memory
The effect of caffeine on short-term memory is debated amongst academics. Studies conclude that caffeine intake improves the performance of short-term and working memory, specifically associating caffeine intake with a shortened reaction time. However, these findings are inconsistent and other studies conclude that caffeine has a detrimental effect on working memory. Increasing memory capacity would result in retaining more information for extended periods of time and encoding information from STM to long-term memory. However, research consensus indicates that caffeine's effect on working memory depends largely on its dosage, and the working memory load.Auditory effects within short-term memory
Caffeine's effects in memory were also investigated in the auditory system. The Auditory-Verbal Learning Test is a memory test that assesses recall of heard lists of words in single and multiple trials. Caffeinated subjects recalled fewer words than control subjects, and caffeinated subjects showed a greater deficit in recalling the middle- to end-portions of the lists.Working memory effects
Caffeine's effects on short term and working memory have been investigated in relation to the tip of the tongue effect. Older research suggests that caffeine decreases the number and duration of tip of the tongue effects by improving short-term memory capacity. More recent research has shown that improved performance attributed to caffeine is due to phonological loop priming, not to general "alertness effects". Subjects were asked to listen to and recall lists of words. The number of tip of the tongue occurrences were counted under two priming conditions: The word lists contained either phonologically similar or phonologically distinct words. Caffeinated subjects had fewer tip of the tongue events when primed with phonologically similar words and a marked increase of tip of the tongue events when primed with phonologically distinct words. The control group showed a significant increase of tip of the tongue events when primed with phonologically similar words, the opposite of the caffeinated group. This led the researchers to conclude that caffeine effects phonological priming rather than memory storage.A study in which caffeinated subjects were tested for recall after fast and slow presentation of word lists found no significant effects of caffeine for male subjects. Female subjects showed decreased recall after slow presentation.
Time-of-day effects
Short-term memory has been thought to be influenced differently throughout the day when caffeine has been ingested. Three groups of caffeine intake were compared during four daytime hours. People with low caffeine intake have a decreased performance later in the day, compared to moderate and a high-level caffeine intake. Thus the effect of caffeine on short-term memory can differ due to many other factors and thus cannot be instantly generalized.State Dependent Memory
Caffeine users are subject to state dependent memory effects when under the effects of caffeine. For example, a study tasked two groups of subjects to remember word lists; half of them had caffeine while the other half were given placebos. When brought back the next day, each original group was now split in half, half of them given the same treatment they were encoded under, the other half given the opposite treatment. Ultimately the study showed that subjects that were under the same treatment in both encoding and retrieval outperformed the other groups. This study does not support a decline or enhancement in working memory due to caffeine but rather a state-dependent effect instead.Long-term memory
Caffeine has been shown to have positive, negative, and no effects on long-term memory. When studying the effects of this and any drug, potential ethical restraints on human study procedures may lead researchers to conduct studies involving animal subjects in addition to human subjects.Positive effects of caffeine on long-term memory
Positive effects of caffeine on long-term memory have been shown in a study analyzing habitual caffeine intake of coffee or tea in addition to consuming other substances. Their effect on cognitive processes was observed by performing numerous cognitive tasks. Words were presented and delayed recall was measured. Increased delayed recall was demonstrated by individuals with moderate to high habitual caffeine intake as more words were successfully recalled compared to those with low habitual caffeine intake. Therefore, improved performance in long-term memory was shown with increased habitual caffeine intake due to better storage or retrieval. A similar study assessing effects of caffeine on cognition and mood resulted in improved delayed recall with caffeine intake. A dose-response relationship was seen as individuals were able to recall more words after a period of time with increased caffeine. Improvement of long-term memory with caffeine intake was also seen in a study using rats and a water maze. In this study, completion of training sessions prior to performing numerous trials in finding a platform in the water maze was observed. Caffeine was consumed by the rats before and after the training sessions. There was no effect of caffeine consumption before the training sessions; however, a greater effect was seen at a low dosage immediately afterward. In other words, the rats were able to find the platform faster when caffeine was consumed after the training sessions rather than before. This implies that memory acquisition was not affected, while increases in memory retention were.Negative effects of caffeine on long-term memory
Researchers have found that long-term consumption of low dose caffeine slowed hippocampus-dependent learning and impaired long-term memory in mice. Caffeine consumption for 4 weeks also significantly reduced hippocampal neurogenesis, a process by which the brain creates new neurons to assist in memory retention, compared to controls during the experiment. The conclusion was that long-term consumption of caffeine could inhibit hippocampus-dependent learning and memory partially through inhibition of hippocampal neurogenesis.In another study, mice were introduced into a lighted box with a dark box attached. Mice are naturally drawn to the dark but entering the dark box would cause them to receive an electric shock. Caffeine was given before the task in doses ranging from 11.55 mg/kg to 92.4 mg/kg. The next day, the mice were reintroduced into the apparatus and their delay in entering the dark box was measured. Caffeine administered at high doses correlated to a decrease in delay from 180 seconds to 105 seconds. Lower doses of caffeine had no significant effect. Linear regression analysis suggested a dose-response relationship between caffeine intake and dark box avoidance.