Something new under the sun has been discovered! Novel findings are frequently associated with new technologies. Such was the case at hand. By utilizing a sophisticated computer algorithm that identified the simultaneous firing of geographically disparate nerve cells in human brains, a new functional brain system was identified. It is referred to as the "Default Mode Network" (DMN).  Examples of existing, well understood neural systems include the oculomotor system (that keeps our eyes tracking together in a way that focuses the visual image on the fovea, the central part of the retina where detailed image processing is performed), the auditory system (that allows us to make sense of the sounds we hear), the visual system (that enables us to compose a visual image from the electrical responses generated when light contacts our eyes) and the somato-motor system (that allows us to perform coordinated motor tasks such as writing and walking).

The anatomic underpinnings of the DMN comprise a disseminated group of nodes connected electrically by long, thin nerve fibers. Think of them like cities linked by superhighways. What fascinated researchers from the outset was the observation that when the brain was engaged in any one of a number of different task-oriented mental chores, the default mode became inactivated. However, during pensive non task-directed moments it became intensely stimulated. Examples of this type of non-task directed mental stimulation include introspective rumination, consideration of self-referential thoughts, reflection about past events, wondering what others might be thinking, mulling over the future, free-associating or what might be referred to as daydreaming. These are some of the most cogent mental functions the brain is called on to perform.

Components of the default mode network include portions of the medial prefrontal cortex and medial parietal cortex (called the precuneus). Not included in the default mode network, but intimately linked to it, is a small, yet vital region called the hippocampus. It plays a pivotal role in processing and calling up memories. A typical, hippocampally mediated association task is the assignment and recollection of the relationship between names and faces.  Being introduced to a stranger and then promptly forgetting his name is the prototypical senior moment. Understanding the role the DM network (especially the precuneus) and the hippocampus play in this frustrating scenario might help prevent it from happening in the future.

Let's walk through a typical social encounter. Consider a block party where there is a large crowd of unfamiliar people, noise and energy, and then throw in the anxiety and stress of meeting a host of new neighbors. For many persons this setting constitutes the "Perfect Storm" of circumstances that foment forgetting, especially when one's memory is not in top form to start with. What happens when you are tasked with remembering your next door neighbor's sister's name involves several steps. Number one is the deactivation of the DM system. This requires conscious input. You must clear your mind of the events of the day, what you need to do after the party, who else might be attending, what their agenda is and so forth. Some times it is helpful to use a note pad to write down what you need to buy at the grocery store, and to free up mental energy for other tasks such as remembering new names. Stress and anxiety make it difficult for the DM to disengage, as does sleep deficiency. When this is the case, the brain must "juggle' many mental balls simultaneously (default mode threads as well as the task at hand). Much like any multi-tasking situation, you probably perform poorly at each of the multiple things you try to do. So, freeing up your mind (allowing your DM to relax) is the first step to remembering.

The next thing that is required is to activate your hippocampus. That involves focusing your attention on the task at hand. You must concentrate, get actively engaged and remain focused. Start out by looking directly into the eyes of the person you have been introduced to. This issues a directive to your brain that this person is a high priority and must be attended to. After learning his name, repeat it to yourself and then again out loud by saying something like, "Frank, it is a pleasure to meet you. I have heard so much about you from you sister." This reinforces the connection and strengthens the memory trace you are establishing.

So hopefully the next time you find yourself in this type of social circumstance, you will think about what cutting-edge science has taught you about senior moments and how to avoid them. Just remember, that to remember you must turn off the default mode and turn on the hippocampus. 

 

Patients receiving chemotherapy for various types of cancer have long complained about neurological side effects they believed were related to the chemo treatments themselves. These symptoms included memory loss, headaches, difficulty concentrating, word-finding problems, mental fatigue and even learning disabilities. Until recently, these complaints were often dismissed as being unrelated to the chemotherapy. Doctors felt they were due to depression about being sick, having cancer, eating poorly, being stressed out, disturbed daily schedules or even "ICU syndrome." However, emerging information is documenting the full scope of the adverse cognitive impact chemotherapy has on the brain. 

In some studies, upwards of 80% of patients treated with chemotherapy reported that they suffer from some form of impaired cognition. This has come to be referred to as "Chemo Brain." These (usually delayed) consequences can compromise the quality of life in a significant portion of cancer survivors. Consistent with these observations is new research demonstrating that treatment with a single chemotherapeutic agent, 5-fluorouracil (5-FU), even when used by itself is able to cause a syndrome of delayed degeneration within the nervous system. 5FU is a widely prescribed chemo drug frequently used in combination with other agents for the treatment of many cancers including cancers of the colon, rectum, breast, stomach, pancreas, ovary and bladder.

Little is known about the brain-related side effects of chemotherapy. Why one patient may be affected and not another is not fully understood. Questions remain including whether these effects are related to dosing regimens, combinations, relationship to specific cancer types, prior brain damage, breakdown of the blood-brain barrier or inflammation. Researchers at the University of Rochester and Harvard Medical School demonstrated in mice studies that administration of 5-FU caused both acute central nervous system damage as well as damage that worsened over time. They discovered this damage was not self repairing. One of the manifestations was an impairment in the rate at which the animals were able to process information.

In addition to toxicity to the dividing cells within the brain, 5-FU damaged cells called oligodendrocytes. They are brain cells responsible for producing the myelin sheath of neurons. This is like the plastic coating on a lamp cord. When damaged, the wires short out and the lamp doesn't work. The same thing happens in the brain. Messages between nerve cells can't be transmitted.

In other studies, Mark Noble, PhD, exposed several different types of healthy brain cells as well as a variety of human cancer cell lines to three commonly used chemotherapy drugs - carmustine, cisplatin and cytosine arabinoside - at levels characteristically experienced in patients. These drugs are used to treat certain types of breast cancer, lung cancer, colon cancer, Hodgkin and non-Hodgkin lymphoma, leukemia and brain tumors.

Cancer treatments are partially based on the assumption that the drugs are less toxic to normal cells than to cancer cells. Normal cells also usually recover more rapidly from chemo than do cancerous cell types. It thus came as a big surprise that these drugs were far more toxic to healthy brain cells than to the cancer cells. Worse still, these drugs were found to be toxic to both non-dividing cells, dividing stem cells and precursors at even very low concentrations. Because neurogenesis (formation of new nerve cells) occurs in the hippocampus - a major hub in memory function - and it is interrupted by these drugs, this locus might be one area where the cognitive side effects of chemotherapy arise.

These findings provide some scientific rationale for the cognitive symptoms many patients receiving chemotherapy describe. However, because chemotherapy is a cornerstone of cancer treatment, no one should forego this potentially life-saving therapy. It should be discussed with your doctor ahead of time and mental function should be monitored during and after therapy. This information should also stimulate the development of strategies to protect brain cells from these drugs.

 

 

The principal mental disorders affecting late life are dementias such as Alzheimer disease (AD) and the primary mood disorder, depression. In addition to cognitive falloff, some of the most common symptoms in the dementing and neurodegenerative diseases are depressed mood, apathy and anxiety. There is overlap between these symptoms and those seen in depression. Loss of neurons and nerve cell connections is characteristically seen in AD. Many investigators have theorized that neuronal atrophy and death in these disorders results, in part, from a lack of of trophic support. For healthy existence, cells in every location in the body depend on chemicals called trophic factors that protect them and allow them to function optimally. In the brain, neurotrophins are the compounds neurons rely on for this cellular support. The primary one is called BDNF (Brain-Derived Neurotrophic Factor). BDNF is present in the highest concentrations in the hippocampus, a brain region with vital functions in both learning and memory.

Hippocampal BDNF levels fall in response to stress.  Stress plays a key role in the development of depression and other psychiatric illnesses. Shrinkage of the hippocampus associated with nerve cell loss and atrophy has been observed in animals exposed to chronic stress. These animals manifest behavioral alterations associated with a depressive state. Consistent with these observations is the fact that humans with a history of chronic, recurrent depression, or post-traumatic stress disorder have shown significant hippocampal atrophy (shrinkage) in brain imaging studies.

One approach used in treating depressive symptoms is the administration of antidepressant medication. Recent evidence suggests that these drugs produce a downstream elevation of BDNF in association with their mood elevating properties. In this context, it is interesting to note that current research studies provide evidence that our daily behavior and lifestyle choices influence the level of BDNF expression in the brain. Exercise and participation in an enlightened environment are often linked with up-regulation of synthesis of this important neurotrophin. They also modulate neurogenesis, or production of new nerve cells within the hippocampus.

The ability of exercise to improve the psychiatric status of depressed patients has been observed for some time. As has already been discussed in previous posts, physical activity upregulates the production of BDNF. This suggests that exercise and antidepressant therapy activate similar molecular pathways in the brain. 

Three recent articles have assessed the effects of exercise on patients with major depressive illness. Several conclusions can be made from these studies. One, that exercise improves the symptoms of depression. Second, exercise improves the outcome in patients being treated with antidepressants. Third, moderate intensity exercise is more effective than low intensity exercise in alleviation of depressive symptoms.

Another significant observation regarding the impact of exercise on depressive symptomatology is that its antidepressant effects endure after the period of exercise is terminated. Effects of depression on executive function are exceedingly problematic for many depressed patients. Exercise has been shown to improve reaction times and other parameters of executive function.

There are very few downsides to exercising. It is good for prevention of obesity, blood pressure control, improvement of cardiovascular risk profile and now it is known to be beneficial for mental health and cognition.

 

Most studies investigating the relationship between various types of exercise and brain function are focused on its effect on Alzheimer disease risk, memory loss associated with aging or chronic impact on various cognitive functions. Rarely have investigations been concerned with changes related to an acute bout of exercise on cognitive function.

As we have seen, an endogenous substance that plays a central role in the health of neurons is brain-derived neurotrophic factor (BDNF). Acting via CREB (Cyclic AMP Response Element Binding Protein), BDNF can produce improvements in a finding called long term potentiation (LTP) which is a physiologic correlate of memory. Exercise training in animal studies is associated with elevation of BDNF. BDNF produces enhanced connectivity between nerve cells that improves brain function. Human studies have not examined biochemical compounds involved in acute exercise-induced improvements in cognitive function. A recent human trial investigated the effects of acute exercise on BDNF levels in blood and their relationship with associated cognitive functional improvements.

The exercise protocol involved riding an bicycle in an exercise physiology lab for about 30 minutes. Cognitive testing was done using the Stroop Test. It requires the subject to read 100 words as fast as possible. The words are "RED", "GREEN" or "BLUE". Each word is a different color, either red, green or blue but the color and the word can not be the same such as RED and the color red. Thus the word RED could be printed in green or blue ink, but not red ink. The test requires the subject to say the color of the word, not what the letters spell. Hence the word BLUE, printed in green, would require a response of "green". The greater the number of correct responses, the better the score.

BDNF levels were measured before the cycling and immediately thereafter.  BDNF levels were elevated 13% after the single exercise trial compared to baseline levels. The Stroop Test results also improved significantly after the cycling. This study demonstrates that strenuous physical activity induced a simultaneous increase in blood BDNF concentrations and function on the Stroop Test. It should be mentioned that in animal studies there is a close correlation between brain and blood BDNF changes after exercise implying that the changes of BDNF measured in blood are reflected in the brain..

Since BDNF has also been associated with enhanced learning in animal studies, in conjunction with the current findings cognitive activities following strenuous exercise might be expected to produce similar findings. This suggests possible mechanisms for orchestrating exercise and mentally challenging tasks for improved results. 

 

Physical activity has been associated with many healthy benefits including reductions in cardiovascular disease, colon and breast cancer, diabetes and obesity. Despite these robust effects, 75% of adults in the United States do not meet currently recommended guidelines for exercise. Estimates indicate that such inactivity was associated with health costs of $76 billion dollars in the United States in 2000. In addition to the physical and economic impact of a sedentary lifestyle, there is an emerging body of scientific research suggesting a connection between exercise and improved brain health and function. Although most of the investigations have evaluated aging humans, some recent studies have investigated the impact of physical activity on cognitive performance in children.

A meta-analysis of studies in school-age children found a positive relationship between level of activity and a number of measures of cognition (perceptual skills, IQ, achievement, verbal tests, math tests, memory, developmental level and academic readiness).

Recently, primarily due to the importance placed on standardized testing, many schools have reduced or done away with physical education (PE) requirements in an effort to ostensibly increase available time for scholastic pursuits. At odds with this mindset are recent studies indicating that performance on standardized tests of mathematics and reading were related to physical fitness scores. Fitness is linked to functioning of the fronto-parietal parts of the brain so it is not surprising that both math and reading elicit activation in this same neural network.

In adults, results from similar types of meta-analyses investigating exercise and cognitive processing reveal several key findings. First, physical activity has a beneficial impact on cognition. Second, chronic activity improves function in both normal adults and patients with early signs of Alzheimer disease. Third, exercise positively affects a broad range of cognitive variables. Fourth, the degree of improvement varies among mental modalities with some (such as executive control processes including scheduling, working memory, multi-tasking and dealing with ambiguity) showing disproportionately larger effects. This is exciting since these executive functions, and the brain regions that mediate them, tend to show age-related deterioration and these findings suggest that such changes may be amenable to intervention.

Consistent with these conclusions, MRI (Magnetic Resonance Imaging) studies have been used to asses the effects of fitness on brain anatomy. Typical findings reveal that higher levels of activity are associated with larger volumes of grey matter in the prefrontal and temporal brain regions as well as increased volume in the anterior white matter. These observations are important because such increases are predictive of better performance in older adults.

Taken together, these data suggest that physical activity can have beneficial effects throughout the lifespan, even for individuals with neurodegenerative disease. Animal studies in this field have documented increased angiogenesis (number of blood vessels) and enhanced formation of synapses (the connections between nerve cells) and neurogenesis (formation of new nerve cells). Decreases in each of these measures have been documented in Alzheimer brains. Hence, researchers appear to be telling us that breaking a sweat on a regular basis is a tonic for our brain.

 

 

Acetylcholine is a neurotransmitter compound (brain chemical that allows nerve cells to speak with one another) associated with memory function. The link between acetylcholine levels in the brain and memory function is so tight that a group of medications mimicking the effect of acetylcholine are used as drugs for memory disorders, dementia and Alzheimer disease (AD). Hence, the findings of CDR Jack Tsao, USN, associate professor for the Uniformed Services University of the Health Sciences' (USU) Department of Neurology linking the use of anti-cholinergic (meaning drugs that block the action of acetylcholine and related compounds) drugs such as medications used in the treatment for stomach cramps, ulcers, motion sickness, overactive bladder and other conditions, to a more rapid decline in cognitive ability in older people comes as no surprise.

His study investigated the effects of consumption of medications with anti-cholinergic actions on the mental status of 870 Catholic nuns and clergy members who were about 75 years old.They underwent annual cognitive testing. In the study, 679 people took at least one medication with anti-cholinergic activity. The results revealed an association between the use of these medications and a decline in cognitive function that was 1.5 times as rapid as those who did not take the drugs.

"Our findings point to anti-cholinergic drugs having an adverse impact on cognitive performance in otherwise normal, older people," said Jack Tsao, M. D. "Doctors may need to take this into account before prescribing these commonly used drugs." Tsao noted that more research is required to define the exact mechanisms responsible for the rapid memory loss apparently associated with anti-cholinergic drugs and to identify which drugs were the primary offenders.

The study concept arose when one of the lead authors, Kenneth Heilman, M. D.,was evaluating a patient with memory complaints and hallucinations. Her cognitive testing was essentially normal with the exception of some memory issues. She didn't fit the criteria for Alzheimer-type dementia. However, she had just begun therapy with tolterodine (Detrol) a drug used to treat over-active bladder and urinary incontinence. After stopping the medication, her memory problems improved. When they reviewed the medical literature, they found that many medications that are not advertised as anti-cholinergic actually have anti-cholinergic properties when tested.

Anti-cholinergic medications range from the overactive-bladder drugs to anti-Parkinsonian agents, anti-spasmodic drugs for the bowel, ulcer medicines, antihistamines and other drugs with less well-known anti-cholinergic activity including lasix, coumadin and ranitidine (Zantac). Examples of some of these drugs are as follows:

Clidinium (Quarzan)

Dicyclomine (Bentyl)

Oxybutynin (Ditropan)

Amitriptyline (Elavil)

Imipramine (Tofranil)

Carbamazeine (Tegretol)

Cyclobenzaprine (Flexeril)

Orphenadrine (Norflex)

Trihexyphenidyl (Artane)

Benztropine (Cogentin)

Chlorpheniramine (Chlortrimeton)

Brompheniramine (Dimetane)

Cyproheptadine (Periactin)

Diphenhydramine (Benadryl)

Chlorpromazine (Thorazine)

Olanzapine (Zyprexa)

Transderm Scop (Scopolamine)

Solifenacin (Vesicare)

Check with your health care provider to see if there are alternatives to these drugs if any of these names are medications you are taking.

 

The cognitive abilities of older persons vary dramatically. There are tell tale signs in the brain that doctors use to make a definitive diagnosis of Alzheimer Disease (AD). These are referred to as "plaques" and "tangles." When they achieve a threshold degree and distribution, the neuropathologist doing the examination establishes that the brain findings are consistent with the diagnosis of AD. Interestingly, it has been established in many studies that approximately 40% of the subjects whose brains house this degree of pathology on post mortem exam have no evidence of mental impairment. This suggests that some brains are able to tolerate these potentially devastating findings much better than others. The "Million Dollar Question" is why. At present, the neurobiologic basis for this robust observation is not well understood.

The concept of "compensation" is commonly applied to many organ systems throughout the body and is an important determinant of health outcomes. When a relative donates a kidney, for example, the donor experiences no loss of renal function because of the large amount of reserve function in the remaining kidney. Hence, it easily compensated for the loss of its neighbor. The only change observed is that it may enlarge slightly over ensuing months due to enhanced physiologic demands. Is it possible that similar changes can occur in the brain.

Brain transplants have not been performed, at least yet. However, interesting findings noted on functional brain scans such as PET (Positron Emission Tomography) scans and fMRI (functional Magnetic Resonance Imaging) scans suggest there is an innate ability of one part of the brain to compensate for diminished function elsewhere. Thus, the brain, de facto, has a component of brain reserve. This is consistent with the notion that the functional organization of the brain is felt to be redundant. In addition, it has been postulated that there are differences between brains in their efficiency and ability to respond to certain environmental challenges.

Neuroimaging data of the type just mentioned support this view. When performing a cognitive task, aging is associated with lower activation of brain regions used by young subjects while performing the same task, and increased activation in other regions. This phenomenon has been interpreted as demonstrating compensation by alternate networks. Surprisingly, a similar pattern of brain activation has been observed in both young patients with mild AD and older subjects without AD. The implication is that the process of compensation (manifested by the engagement of additional brain resources) is a normal process during aging and in pathologic states such as AD (and presumable stroke, head injury and other disease states).

The concept of brain reserve was first referenced in a study of individuals with high levels of AD pathology post mortem who remained nondemented in life and had almost twice the number of neurons throughout their cerebral cortex in comparison to those who developed mental symptoms. It was felt that "those people might have started with a larger brain and more neurons and thus might be said to have a greater reserve."This neurocentric version of reserve relies on a genetically endowed advantage based on increased neuronal numbers.

Another perspective regarding brain reserve involves the concept of "neurocomputational flexibility" wherein certain individuals who have developed a range of cognitive strategies for solving complex problems are more likely to remain normal cognitively for longer despite progression of underlying disease. They may also have a greater number of potential neural pathways for execution of these cognitive processes, thus permitting maintenance of function despite neurological insult. In essence, this suggests that an individual who utilizes a specific brain network more efficiently, or is able to bring alternative brain networks on-line in response to increased demand may thus have greater brain reserve. Such a construct links brain reserve with performance of complex mental activities, increased neural and synaptic (a synapse is the point where one nerve cell contacts another) numbers and consequently enhanced brain function.

Numerous population-based cohort studies have examined the link between complex mental activity and risk of developing dementia. When analyzed together, they revealed an overall risk reduction of 46%. The separate effects of education, occupational complexity and cognitive lifestyle activities were similar in magnitude. The issue is whether such mental activity-related dementia risk remains modifiable in late life. Interestingly, participation in cognitive and social lifestyle activities in later life (independent of either education or occupational experiences) showed significant (50-66%) protection against risk of dementia.

What are the possible mechanisms behind this robust effect? Mental stimulation is a strong stimulator for the generation of a neurochemical called BDNF (Brain-Derived Neurotrophic Factor) and Nerve Growth Factor (NGF). They play critical roles in nerve cell survival, neuronal connectivity, resistance to disease and learning and memory. An enriched mental environment increases generation of new synapses by 150-200%. This effect is especially important for dementing illnesses because of the dramatic loss of synapses in these disorders. Even more intriguing is the suggestion that mental activity may diminish the production of AD neuropathology. These insights are potent incentives to engage in a mentally active lifestyle to ensure a vibrant future life.

During the billions of years of human (and pre-human) evolution, time has been divided into daily, seasonally, and yearly repeating cycles. Based on these imposed cycles, biological processes have developed that have enabled organisms to exploit temporal niches in their environment and to coordinate physiological responses to optimize metabolic efficiency and survival.

In humans, because of evolutionary pressures, these rhythms have become entrained within our nervous systems. They are generated by the approximately 20,000 neurons located in the master clock in the suprachiasmatic nucleus (SCN) of the brain. It’s proximity to the optic nerves (the nerves connecting the eyes to the brain) is not surprising given the role the day-night (light-dark) cycle plays in this physiology. Its nexus with a part of the brain called the hypothalamus, the region that monitors and controls the body's internal milieu (fluid and electrolyte balance, temperature regulation, and hormonal status, etc.) has important implications as well.

The pacemakers for these rigidly regulated functional ebbs and flows are generated endogenously within the network of SCN nerve cells. More interestingly, each cell in this grouping has intrinsic clock-like abilities incorporated within its genetic makeup. Specific genes (referred to as clock genes) generate the rhythm. This is done using a biological trick called a negative feed back loop. It works as follows. The gene turns on and does what genes do. That is, it creates a protein that is released within the cell. Among other duties, this protein then interacts with the gene that created it and in so doing, turns it off. This process is repeated over and over again. The time it takes for one complete cycle is 24 hours. This nifty process constitutes the molecular basis for the biological clock that forms the basis for the circadian (within a day) cycles that coordinate many bodily processes. Circadian rhythmicity is abolished by damage to the SCN.

These clock genes, and their associated daily cycles, are genetically conserved over numerous species. They play vital roles in many biological phenomena including metabolism, hormonal regulation, fertility/reproduction, thermoregulation, bone formation, fat accumulation and sleep-wake cycles. As such, alterations in circadian periodicity might affect these processes. Mood disorders are even associated with rhythm disruption and clock gene variations. Under conditions of constant light or constant darkness, the synchronicity of the SCN neurons is lost. “Jet lag” seems to be a likely consequence of this environmentally induced perturbation. The advent of the “24 hour society” likely has had adverse impacts on the SCN and probably contributes to the prevalence of sleep disorders estimated to affect 20% of Americans.

In the regulation of hormonal function, timing is everything. This depends intimately on the internal clock mechanism that orchestrates the synthesis, secretion and control of hormones. It is well-known that differing exposure to light modulates hormonal regulation and melatonin levels. Other environmental stimuli such as social signals, poor nutrition, physical activity levels, sleep habits and stress produce effects that are integrated in to the functioning of this intricately balanced system. Common examples of adverse effects are altered menses, infertility, mood swings and difficulty concentrating and learning. Cortisol, the “stress” hormone can single-handedly reset the circadian clock.

It should be obvious that changes in many of the factors discussed above can induce functional alterations in our biological clock mechanism producing adverse health changes in many bodily systems.