People and animals can rapidly learn to associate environmental stimuli with positive or negative outcomes, learning what to approach or avoid as they go through daily life. The amygdala plays a role in this type of emotional learning, which can be disrupted by mood disorders. In new research, Praneeth Namburi and colleagues determined that activity at the synapses in the basolateral amygdala reveals differences in the creation of fear memories and reward memories.
In animals trained with reward and fear conditioning tasks, photostimulation of neurons that then travel from the basolateral amygdala complex to the nucleus accumbens (the brain’s reward center) is positively reinforcing, while photostimulation of neurons that will travel from the basolateral amygdala complex to the centromedial nucleus of the amygdala causes aversion. There are genetic differences between the two types of neurons, including a difference in the gene for the neurotensin-1 receptor. The researchers found that neurotensin, a neuropeptide, modulates glutamate’s effect on neurons, causing some to project to the nucleus accumbens and some to project to the centromedial nucleus of the amygdala.
The researchers wrote that the results “provide a mechanistic explanation, on both a synaptic and circuit level, for how positive and negative associations can be rapidly formed, represented, and expressed within the amygdala.”
Editor’s Note: The amygdala’s creation of opposing outputs may provide clues to the mechanisms behind mania (involving the nucleus accumbens) and depression (involving the centromedial nucleus of the amygdala).
Events like surgery or heart attacks that cause inflammation can lead to cognitive deficits or depression for months or years afterward, even though the direct effects of inflammation wear off within weeks. In a recent study, Natalie Tronson and colleagues subjected mice to surgical heart attack, sham surgery, or no operation, and observed how well they absorbed new learning eight weeks later.
Both male and female mice had impairments in fear learning following surgical heart attacks. Female mice that received sham surgery also showed deficits in fear learning. When the researchers dissected the mice, analyzing their blood and hippocampi after the eight-week period, inflammatory cytokine measures had normalized as expected, but the researchers found other abnormalities.
Intracellular signaling was dysregulated, and there had been epigenetic changes in cells of the hippocampus. (Epigenetic changes refer to those that change the structure of DNA, such as how tightly it is wound, rather than its sequence. For example, the addition of acetyl groups to DNA or the histones around which it is wound.) The researchers observed increased histone acetylation and phospho-acetylation following the heart attacks.
The researchers concluded that a systemic inflammatory event, such as heart attack or surgery, can cause long-term memory impairment and changes in mood through epigenetic mechanisms. They compared the findings to those of other studies in which normal aging and memory-impairing treatments such as chemotherapy had also been associated with increases in histone acetylation or decreases in histone deacetylase activity.
Researcher Amanda Roten reported at the 2014 meeting of the American Academy of Child and Adolescent Psychiatry that adolescents who stopped heavy marijuana use showed improvements in multiple areas of learning and memory. These data support previous findings that pot can cause impairments in cognitive functioning, but that abstaining from the drug can bring about improvement relative quickly.
These data contrast with some others. A 2009 study by J. Jacobus et al. in the journal Pharmacology Biochemistry and Behavior suggested that some changes in brain structure resulting from marijuana use, such as decreases in cortical volume, can persist for one to three months following abstinence.
Madeline Meier, another researcher at the meeting, reported that 1,037 participants who used marijuana persistently from about age 13 to age 38 lost an average of 8 IQ points. Controlling for years of education and other potential confounds such as alcohol and drug use did not affect these findings. Moreover, Meier found that “cessation of cannabis use did not fully restore IQ among adolescent-onset cannabis users.”
Editor’s Note: The popular view that marijuana is a benign substance overlooks some key facts. The main pharmacological effect of pot is an amotivational syndrome, causing apathy and lack of drive to participate in work, study, and other activities. Heavy use of pot doubles the risk of psychosis, and this risk is further increased if a user has a common genetic variation in the enzyme catechol-o-methlyl transferase (COMT), which metabolizes dopamine. The more efficient allele of COMT (known as val-56-val, identifying two valine amino acids) lowers frontal cortex dopamine more, and increases the risk of delusions and hallucinations. Marijuana alters brain structure and impairs memory. It may now be legal in some states, and while reducing penalties for smoking marijuana may be a good idea, this does not mean the drug is a harmless substance.
The moral of the story is that avoiding marijuana use in the first place, especially for people with bipolar disorder, should make it easier to get well and stay well. For current marijuana users, N-acetylcysteine (NAC, a nutritional supplement available without a prescription from health food stores) has been shown to help adolescents decrease marijuana use more than placebo.
Flavanols, which are found in small amounts in raw cocoa, tea leaves, fruits, and vegetables, may be able to improve age-related memory loss. The normal process by which chocolate is made removes all flavanols from cocoa, but the Mars Inc. company recently developed a process to isolate flavanol in powder form.
In a 2014 study by Scott Small et al. in Nature Neuroscience, of 37 participants between the ages of 50 and 69, those who were randomized to a high-flavanol diet (900mg per day, from drinking the powder mixed with water or milk) over a three-month period showed more improvement on a memory test than those participants who were randomized to a low-flavanol diet (10mg per day). The high-flavanol group both scored higher than the other group at the end of the study and showed more improvement relative to their own abilities at the start of the study. Small said that after three months of taking the flavanols, someone who began with a typical memory for a 60-year-old developed a memory more like a 30- or 40-year-old. The high-flavanol group also showed improvement in function in a part of the hippocampus called the dentate gyrus.
Like cancer patients undergoing chemotherapy, patients with bipolar disorder often have memory problems, particularly if they have had many prior episodes. Some memory tips from CancerCare’s Chemobrain Information Series may also help patients with bipolar disorder remember things better and keep their memory sharp. Here are some of their tips:
Make lists. Carry a notepad with you, or use a smartphone to keep track of errands, shopping lists, daily tasks, and when you should take your medications.
Use a paper or electronic day planner or a personal organizer to keep track of appointments and special days like birthdays or anniversaries.
Use a wall calendar and hang it in a place that you will see it multiple times per day.
Carry a notebook and record everything you need to remember, including to-do lists; the dates, times, and addresses of appointments; important telephone numbers; and the names of people you meet and a brief description of them. You can also use the notebook to keep track of medical information: your medication schedule, any symptoms or side effects you are having, or questions to ask your doctor. You can also do this using an app like What’s My M3 or by downloading a personal mood charting calendar from our website.
Leave yourself a voicemail message to remember something important. When you listen to it later, write down the information.
Organize your home or office. Keep things in familiar places so you always know where to find them.
Avoid distractions. Find a quiet, uncluttered place to work or think where you can focus your attention for longer.
Have conversations in quiet places. This will help you concentrate better on what the other person is saying.
Repeat information aloud, and write down important points. If someone gives you information about an appointment, you might repeat the time, date, and location of the appointment out loud while righting it down.
Keep your mind active. You can use crossword puzzles, word or math games, or attend events about topics that interest you.
When writing, proofread. Double-check whether you’ve used the correct words and spellings.
Train yourself to focus through mindfulness. For example, if you keep misplacing your keys, pay extra attention each time you set down your keys. You may say aloud, “I’m putting my keys down on the counter.” Hearing the auditory cue can boost your memory.
Exercise, eat well, and get plenty of rest and sleep. These habits will help your memory work best.
Tell your loved ones that you are having memory problems, so that they’ll understand that you may forget things you may normally be able to remember. They can help you or encourage you.
Omega-3 fatty acids (especially the type known as DHA) are essential for brain development and functioning, but most people eating a modern western diet consume low amounts of these compared to omega-6 fatty acids. Omega-3s are anti-inflammatory while omega-6s are pro-inflammatory. A large UK study published in the journal PLOS One in 2013 reported that healthy 7- to 9-year-olds with lower levels of omega-3 long-chain polyunsaturated fatty acids in their blood (including DHA, DPA, and EPA) had lower reading ability and working memory, and also had more behavior problems.
The oils in fish are the best source of omega-3 fatty acids, and most of the children with poor reading ability in the study fell short of the UK nutritional guideline that recommends eating two portions of fish per week.
Girls in the study had more dramatic deficits in omega-3 levels than boys. In adults, women tend to metabolize long chain polyunsaturated fatty acids more easily than men, but this difference is driven by hormones, and because the girls in the study had not yet reached child-bearing age, they did not reflect this benefit.
Omega-3 deficits in children have been connected with attention deficit hyperactivity disorder (ADHD), and supplementation with extra omega-3 fatty acids in the diet has led to improvements in ADHD.
In a 2014 study published by Michael A. Yassa et al. in the journal Nature Neuroscience, a 200mg caffeine pill (about the equivalent of a strong cup of coffee) improved long-term recognition memory. One hundred sixty participants who were not regular coffee drinkers were shown a series of 200 pictures, and 24 hours later they were given a surprise test. Compared to participants who received a placebo, those participants who received 200mg of caffeine were better able to discriminate which pictures they had seen before and which ones were new. Participants who received 100mg of caffeine did not show this effect, while those who received 300mg showed the same improvement in memory but also experienced side effects such as headache and nausea.
As long as a cup of coffee does not make its drinker more anxious, it may help boost memory.
Editor’s Note: Coffee may have other benefits. In research collected by the Bipolar Collaborative Network (in which this editor is an investigator), patients who drank coffee were less likely to be overweight. Yassa also believes based on other research that caffeine is associated with a reduced risk for Alzheimer’s disease and that it increases longevity.
Exercise increases brain-derived neurotrophic factor (BDNF), a protein that protects neurons and is important for learning and memory. In a study of mice who were trained to find objects, sedentary mice could not discriminate between familiar object locations and novel ones 24 hours after receiving weak training, while mice who had voluntarily taken part in exercise over a 3-week period could easily distinguish between these locations after the weak training.
Mice who received sodium butyrate (NaB) after training behaved similarly well to those who had exercised. Sodium butyrate is a histone deacetylase (HDAC) inhibitor, meaning it helps keep acetyl groups on histones, around which DNA is wrapped, making the DNA easier to transcribe. In this case the easy transcription of DNA enables learning under conditions in which it might not usually take place.
Both sodium butyrate and exercise promote learning through their effects on BDNF in the hippocampus. They make the DNA for BDNF easier to transcribe, suggesting that exercise can put the brain in a state of readiness to create new or more lasting memories.
Unwanted recall and re-experiencing of traumatic memories is thought to be a crucial mechanism leading to the onset of post-traumatic stress disorder (PTSD). The inability to diminish (extinguish) those memories contributes to the persistence of PTSD. A new study suggests that the extinction of fear memories can be enhanced by a drug that acts epigenetically to alter the structure of DNA and subsequent gene expression.
DNA is wound around structures called histones, and chemical changes can affect how loosely or tightly the DNA is wound. Johannes Graff et al. reported in the journal Cell in 2014 that application of a histone deacetylase (HDAC) inhibitor, which keeps acetyl groups on histones, ensuring that DNA is wrapped more loosely and is easier to activate (or transcribe), helps rodents revise both new and old fear memories after they have been actively recalled.
When a memory is actively recalled, the trace of that memory in the brain becomes more amenable to revision over the proceeding five minutes to one hour (a period known as the reconsolidation window). New learning and extinction training (to get rid of the memory) lasts much longer when it takes place during the reconsolidation window than when the same procedures are performed 6 hours later (after the reconsolidation window has closed) or if the procedures are performed in the absence of active recall of the memory (when the reconsolidation window is never opened).
We have previously described the 2013 work of Xue et al. published in the journal Science, which showed that this specific procedure could yield long-lasting extinction of a patient’s craving for cocaine or heroin, and could reduce amygdala activation (as observed via functional magnetic resonance imaging) in response to an experiment that produces conditioned fear (Agren et al. Science, 2013).
Editor’s Note: This new work by Graff et al. adds another twist. Older long-term memories are more stable and less amenable to new learning than more recent (but still long-term) memories. The application of an HDAC inhibitor changes this and makes even very old memories amenable to lasting revision. The HDAC inhibitor that Graff et al. used was a specific inhibitor for HDAC type II. However, the anticonvulsant valproate (Depakote) is a potent although nonspecific HDAC inhibitor, and presumably could have the same facilitating effect as the more selective drug.
EMDR (Eye Movement Desensitization and Reprocessing), which has been widely used for the treatment of PTSD, includes active memory recall, immediately followed by an attempt to re-interpret and construct new memories of the trauma. These elements could open the reconsolidation window. However, EMDR works less well with older memories compared to more recent traumatic memories.
The Graff et al. data would suggest that adding an HDAC inhibitor such as valproate to EMDR-like work might make it more effective in revising more remote memories. Graff et al. encourage controlled clinical trials with a type II inhibitor to confirm that their findings in rodents would generalize to humans. While awaiting such validation through controlled clinical trials, it would not be surprising if clinicians started trying out the paradigm on their own using valproate.
Brain-derived neurotrophic factor (BDNF) is involved in various aspects of learning and memory. The DNA for BDNF contains nine different regulatory sites, each of which is involved in different aspects of learning. Researcher Keri Martinovich studied each site by selectively knocking each one out with a genetic manipulation. She found that blocking the e1 site increased acquisition of new learning and recall in mice, while e2 did the opposite. Blockade of e4 had no effect on these memory functions but markedly blocked the process of extinction, which involves a different kind of new learning.
A mouse that learned to associate a particular cue with a shock (a process known as conditioned fear) will stop reacting to the cue after it is presented many times without a shock. This learning that the cue is no longer associated with the shock is referred to as extinction. The animals with e4 blocked in their BDNF did not develop the new extinction learning, and continued to react to the cue as if it were still associated with the shock.
Editor’s Note: These data may have clinical relevance for humans. The anticonvulsant valproate (trade name Depakote), a histone deacetylase inhibitor, selectively increases the e4 promoter site of BDNF and facilitates extinction of conditioned fear, according to research by Tim Bredy et al. published in 2010.
Clinical trails should examine whether valproate could enhance fear extinction in patients with post-traumatic stress disorder (PTSD).