At the 2015 meeting of the International Society for Bipolar Disorders, Ben Goldstein described a study of cognitive dysfunction in pediatric bipolar disorder. Children with bipolar disorder were three years behind in executive functioning (which covers abilities such as planning and problem-solving) and verbal memory.
There were other abnormalities. Youth with bipolar disorder had smaller amygdalas, and those with larger amygdalas recovered better. Perception of facial emotion was another area of weakness for children (and adults) with bipolar disorder. Studies show increased activity of the amygdala during facial emotion recognition tasks.
Goldstein reported that nine studies show that youth with bipolar disorder have reduced white matter integrity. This has also been observed in their relatives without bipolar disorder, suggesting that it is a sign of vulnerability to bipolar illness. This could identify children who could benefit from preemptive treatment because they are at high risk for developing bipolar disorder due to a family history of the illness.
There are some indications of increased inflammation in pediatric bipolar disorder. CRP, a protein that is a marker of inflammation, is elevated to a level equivalent to those in kids with juvenile rheumatoid arthritis before treatment (about 3 mg/L). CRP levels may be able to predict onset of depression or mania in those with minor symptoms, and is also associated with depression duration and severity. Goldstein reported that TNF-alpha, another inflammatory marker, may be elevated in children with psychosis.
Goldstein noted a study by Ghanshyam Pandey that showed that improvement in pediatric bipolar disorder was related to increases in BDNF, a protein that protects neurons. Cognitive flexibility interacted with CRP and BDNF—those with low BDNF had more cognitive impairment as their CRP increased than did those with high BDNF.
N-acetylcysteine (NAC) is an anti-oxidant nutritional supplement that has been found to reduce a wide range of habitual behaviors, including drug and alcohol use, smoking, trichotillomania (compulsive hair-pulling), and gambling. It also improves depression, anxiety, and obsessive behaviors in adults, as well as irritability and repeated movements in children with autism. A new study suggests NAC may also be able to reduce non-suicidal self-injury, often thought of as “cutting,” in girls aged 13–21.
The open study, presented in a poster by researcher Kathryn Cullen at the 2015 meeting of the Society for Biological Psychiatry, compared magnetic resonance imaging (MRI) scans of 15 healthy adolescent girls to scans of 22 girls who had been engaging in self-injury, both before and after this latter group received eight weeks of treatment with N-acetylcysteine. Doses were 1200 mg/day for the first two weeks, 2400mg/day for the next two weeks, and 3600mg/day for the final four weeks. The girls also reported their self-injury behaviors.
Treatment with NAC reduced the girls’ self-injury behaviors. The brain scans showed that NAC also increased resting-state functional connectivity between the amygdala and the insula. Connectivity in this region helps people regulate their emotional responses. At baseline, the girls who engaged in self-harm had had deficient connectivity between the amygdala, the prefrontal cortex, insula, and the posterior cingulate cortices compared to the healthy girls, and this improved with the NAC treatment.
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).
Regulation of the amygdala (the brain’s emotional center), particularly through its interaction with the ventral anterior cingulate cortex, has been implicated in the experience of fear in animals, and anxiety and depression in humans. Connectivity between the two structures is critical for emotion modulation. Repeated transcranial magnetic stimulation (rTMS) is a method of stimulating outer regions of the brain with magnets. Researchers Desmond Oathes and Amit Etkin are investigating whether rTMS can also be used to influence these deeper brain areas, or their interaction with each other.
The researchers’ study used single-pulse probe TMS delivered at a rate of 0.4 Hz at 120% of each participant’s motor threshold, targeted at the anterior or posterior medial frontal gyrus on either side of the brain. The researchers also used functional magnetic resonance imaging (fMRI) of the whole brain to observe connectivity between different sections.
RTMS to the right side of the medial frontal gyrus increased connectivity between the amygdala and the ventral anterior cingulate cortex more than stimulation to the left side. Stimulation of the posterior portion of the medial frontal gyrus increased connectivity more than stimulation of the anterior portion.
Editor’s Note: These data indicate that rTMS can alter brain activity in these deeper regions and can influence inter-regional connectivity. This is important because abnormalities in the connectivity of brain regions have increasingly been found in patients with mood disorders. Oathes and Etkin hope that these findings can be applied to others and that rTMS can be used to correct patterns of regional connectivity in the brain in order to improve emotion regulation.
Researchers have identified neurons responsible for remembering conditioned fear in the amygdala of rodents, and can turn them on and off. At the 2013 meeting of the Society of Biological Psychiatry, Sheena A. Josselyn gave a breath-taking presentation on this process.
When animals hear a tone they have learned to associate with the imminent delivery of a shock in a given environment, they learn to avoid that environment, and they reveal their learning of the tone-shock association by freezing in place. Josselyn was able to observe that 20% of the neurons in the lateral nucleus of the amygdala were involved in this memory trace. They were revealed by their ability to increase the transcription factor CREB, which is a marker of cell activation. Using cutting-edge molecular genetic techniques, the researchers could selectively eliminate only these CREB-expressing neurons (using a new technology in which a diphtheria toxin is attached to designer receptors exclusively activated by designer drugs, or DREADDs) and consequently erase the fear memory.
The researchers could also temporarily inhibit the memory, by de-activating the memory trace cells, or induce the memory, so that the animal would freeze in a new context. Josselyn and colleagues were able to identify the memory trace for two different tones in two different populations of amygdala neurons.
The same molecular tricks with memory also worked with cocaine cues, using what is known as a conditioned place preference test. A rodent will show a preference for an environment where it received cocaine. Knocking out the selected neurons would remove the memory of the cocaine experience, erasing the place preference.
The memory for cocaine involved a subset of amygdala neurons that were also involved in the conditioned fear memory trace. Incidentally, Josselyn and her group were eventually able to show that amygdala neurons were in competition with each other as to whether they would be involved in the memory trace for conditioned fear or for the conditioned cocaine place preference.
In a 2013 study of children by Luby et al. in the Journal of the American Medical Association Pediatrics, poverty in early childhood was associated with smaller white and gray matter in the cortex and with smaller volume of the amygdala and hippocampus when the children reached school age. The effects of poverty on hippocampal volume were mediated by whether the children experienced stressful life events and whether a caregiver was supportive or hostile.
The children were recruited from primary care and day care settings between the ages of three and six, and were studied for five to ten years. They were initially assessed annually for three to six years and information on psychosocial, behavioral, and developmental dimensions were collected. Then the children took part in a magnetic resonance imaging (MRI) scan and continued annual assessments that included information such as whether the children experienced stressful life events.
Previous research has shown that poverty affects children’s psychosocial development and economic success in adulthood. This research shows that poverty also affects brain development. The findings suggest important targets for intervention that could help prevent these developmental deficits.
In articles published in Science in 2007 and 2009, Han et al. showed that about 20% of neurons in the lateral amygdala of mice were involved in the formation of a fear memory, and that selective deletion of these neurons could erase the fear memory. Using the same methodology, Josh Sullivan et al. identified neurons that were active in the mouse brain during cocaine conditioning. Amygdala activity showed that the mice preferred an environment where they received cocaine to an environment where they didn’t. The researchers noticed increased cyclic AMP, a messenger that led to increased production of calcium responsive element binding protein (CREB). When the researchers targeted the neurons in the lateral amygdala that were overexpressing CREB, they found that selective destruction of the overexpressing neurons disrupted the cocaine-induced place preference.
The research team further documented this effect by temporarily, rather than permanently, knocking out neuronal function. They could reversibly turn off neurons with an inert compound that promotes neuronal inhibition. Silencing the neurons that were overexpressing CREB before the conditioned place preference testing also limited cocaine-induced place preference memory.
Editor’s Note: While this type of intervention is not feasible in humans with cocaine addiction, these data do shed more light on the mechanisms behind cocaine conditioning.
We have written before that if extinction training to break a cocaine habit or neutralize a learned fear is performed within the brain’s memory reconsolidation window (five minutes to one hour after memory recall), it can induce long-lasting alterations in cocaine craving or conditioned fear.
It is possible that properly timed extinction of cocaine- or fear-conditioned memories might work similarly to the selective silencing of neurons that was carried out in the mice using a drug that inhibited CREB-activated neurons. Determining the commonalities between these ways of eliminating conditioned memories could lead to a whole new set of psychotherapeutic approaches to anxiety disorder, addictions, and other pathological habits.
At a recent scientific meeting, Jennifer E. Murray et al. presented findings about the amygdala’s role in habitual cocaine seeking. The amygdala is the part of the brain that makes associations between a stimulus and a response. When a person begins using cocaine, a signal between the amygdala and the ventral striatum (also known as the nucleus accumbens), the brain’s reward center, creates a pleasurable feeling for the person. The researchers found that in mice who have learned to self-administer cocaine, as an animal progresses from intermittent use to habitual use, the amygdala connections shift away from the ventral striatum toward the dorsal striatum, a site for motor and habit memory. If amygdala connections to the dorsal striatum are severed, the pattern of compulsive cocaine abuse does not develop.
Editor’s Note: These data indicate that the amygdala is involved in cocaine-related habit memory, and that the path of activity shifts from the ventral to the dorsal striatum as the cocaine use becomes more habit-based—automatic, compulsive, and outside of the user’s awareness.
As we’ve reviewed before, the amygdala also plays a role in context-dependent fear memories, such as those that occur in post-traumatic stress disorder (PTSD). The process of retraining a person with PTSD to view a stimulus without experiencing fear is called extinction training. A study by Agren et al. published in Science in 2012 demonstrated that when extinction training of a learned fear took place within the brain’s memory reconsolidation window (five minutes to one hour after active memory recall), the training was sufficient to not only “erase the conditioned fear memory trace in the amygdala, but also decrease autonomic evidence of fear as revealed in skin conductance changes in volunteers.”
The preclinical data presented by Murray and colleagues suggest the possibility that amygdala-based habit memory traces could also be revealed via functional magnetic resonance imaging (fMRI) in subjects with cocaine addiction. Attempts at extinction of cocaine craving, if administered within the memory reconsolidation window, might likewise be able to erase the cocaine addiction/craving memory trace, as Xue et al. reported in Science in 2012.
In two posters presented at the 2012 meeting of the American Academy of Child and Adolescent Psychiatry, a research group led by Kiki Chang reported that increased severity of manic symptoms is associated with increased size of the amygdala (especially the right amygdala) in adolescents who are at high risk for developing bipolar disorder.
The amygdala is a crucial area for emotion regulation. The increasing size, either with more manic symptoms or as patients with bipolar disorder age into adulthood compared to normal volunteer controls (as we describe in the article on brain imaging at far left) could reflect increased use of the amygdala in bipolar disorder.
The increased amygdala size could be linked to increased emotion dysregulation, or it could be a compensatory mechanism in which the amygdala works harder to exert better emotion control.
Experience-dependent neuroplasticity describes a phenomenon in which the volume of a brain area increases as it gets more use (like a muscle that grows when it gets more exercise). One interesting example in which this may occur is London taxi drivers, who have larger hippocampi than the general public. (The hippocampus is responsible for some of the brain’s spatial recognition abilities.) This could be explained in two different ways. The discrepancy in size between the hippocampi of taxi drivers and of the general population may exist because the taxi drivers’ brains change over the course of their careers via experience-dependent neuroplasticity, or it may exist because those with excellent spatial recognition abilities and bigger hippocampi choose to become taxi drivers.
This editor (RM Post) in collaboration with Jacqueline Fleming and Flavio Kapczinski published the article “Neurobiological mechanisms of illness progression in the recurrent affective disorders” in the Journal of Psychiatric Research this year. The article built on several themes about the progression of bipolar illness that had been explored in previous research.
These themes include:
- The likely acceleration of repeated episodes as a function of the number of prior episodes (episode sensitization)
- The increased responsivity of the illness to repeated stressors (stress sensitization)
- The increased behavioral reactivity to repeated use of psychomotor stimulants such as cocaine (stimulant-induced behavioral sensitization)
Not only are these observations well documented in the scientific literature, but recent observations also suggest that each type of sensitization can show cross-sensitization to the other two types. That is, individuals exposed to repeated stressors are more likely both to experience affective illness episodes and to adopt comorbid substance abuse. In a similar way, episodes of an affective disorder and stressors may also be associated with the relapse into drug administration in those who have been abstinent.
In addition to these mechanisms of illness progression in the recurrent affective disorders, the new article reviews the literature showing that the number of affective episodes or the duration of the illness appear to be associated with a variety of other clinical and neurobiological variables.
The number of affective episodes a patient experiences is associated with the degree of cognitive dysfunction present in their bipolar illness, and experiencing more than 4 episodes of unipolar or bipolar depression is a risk factor for dementia in late life. A relative lack of response to most treatments is also correlated with the number of prior episodes, and this holds true for response to naturalistic treatment in general. While most of these data are correlational and the direction of causality cannot be ascertained for certain, it is likely that the number of affective episodes and/or their duration could account for and drive difficulties with treatment and with cognitive function.
If this were the case, one would expect to see a variety of neurobiological correlates with the number of prior episodes or duration of illness, and in the article we summarize those that have been found in unipolar and bipolar disorder. Considerable data indicate that cortical volume and degrees of prefrontal cortical dysfunction can vary as a function of number of prior episodes. There is evidence that increased activity of the amygdala and the nucleus accumbens are also related to episodes or duration of illness. In those with unipolar depression, the volume of the hippocampus is decreased with longer duration of illness. Read more