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Wednesday, April 22, 2009

Three Ways to Slow Brain Aging

Moderate physical exercise, dietary restriction, and enriched environment stimulation are all known to be good for the brain in general and memory in particular. However, few studies have directly compared these three factors all in the same study, as has been done in the lab of Alois Strasser in the University of Veterinary Medicine in Austria. Moreover, Strasser examined also a brain chemical that is likely to cause some of the brain improvement, the so-called brain-derived neurotrophic factor (BNDF), which sustains neuron life and promotes growth of neuronal processes and synapse formation.

As brain ages, the levels of BNDF typically decline. Several studies have demonstrated that BNDF is important for memory function. Research prior to that of Strasser’s lab showed that exercise “up-regulates” BNDF; that is, exercise stimulates its production. And there had been some indication that environmental enrichment (stimulation, social interactions, etc.) had a similar effect. Therefore, Strasser and colleagues examined the tissue concentrations of BDNF in the cerebral cortex of old rats.

Rats were divided randomly into six groups, living from 5 months up to 23 months. In each age group, rats were divided into those that were given free access to running wheels (RW), forced running on treadmills, food restriction, and sedentary controls with no food restriction. Rats were either either housed individually or in groups of 4 to provide social enrichment. At the end of experiments, BDNF concentrations were determined.

Researchers found higher BNDF concentrations in the 5-month-old animals than in the 23-month-old-animals, suggesting that decline in BNDF accompanies old age and probably accounts for some of the mental decline. Within the older group of rats, sedentary rats that were housed in groups had significantly higher BNDF concentration compared to the old individually caged groups. Their BNDF concentrations were even higher than those of the young baseline group. The results suggest that housing and social interactions have more influence on BDNF concentrations in the cerebral cortex of aging rats than do physical exercise and food restriction.
There was some benefit of the exercise, but only from forced running on the treadmill, not voluntary activity. However, other studies had established that even voluntary exercise by old animals increased BNDF in other parts of brain, including the area so crucial to memory formation, the hippocampus.

The lack of beneficial effect of caloric restriction in sedentary rats to weight levels matching those of the voluntary exercise group was somewhat unexpected. Prior studies in other labs had shown that such restriction does promote synaptic plasticity and even birth of new neurons. Thus, there are no doubt multiple influences that can be beneficial to brain that are not mediated by BNDF. So, to the extent that these results can be extrapolated to aging humans, it would seem like a good idea to:
  1. Exercise regularly and vigorously (assuming you don’t have heart trouble or other conditions that would prevent it)
  2. Lose weight
  3. Get out of the house and socialize.

Strasser, A. et al. 2006. The impact of environment in comparison with moderate physical exercise and dietary restriction on BNDF in the cerebral parietotemporal cortex of aged Sprague-Dawley rats. Gerontology. 52: 377-381.

Increase Working Memory and Increase IQ

A key research report on working memory was summarized in a recent guest column in the New York Times by Sam Wang and Sandra Aamodt. Below is a summary of what they said in the article:

J. R. Flynn first noted that standardized intelligence quotient (I.Q.) scores were rising by three points per decade in many countries, and even faster in some countries like the Netherlands and Israel. For instance, in verbal and performance I.Q., an average Dutch 14-year-old in 1982 scored 20 points higher than the average person of the same age in his parents’ generation in 1952. These I.Q. increases over a single generation suggest that the environmental conditions for developing brains have become more favorable in some way.

What might be changing? One strong candidate is working memory, defined as the ability to hold information in mind while manipulating it to achieve a cognitive goal. Examples include remembering a clause while figuring out how it relates the rest of a sentence, or keeping track of the solutions you’ve already tried while solving a puzzle. Flynn has pointed out that modern times have increasingly rewarded complex and abstract reasoning. Differences in working memory capacity account for 50 to 70 percent of individual differences in fluid intelligence (abstract reasoning ability) in various meta-analyses, suggesting that it is one of the major building blocks of I.Q. (2-4). This idea is intriguing because working memory can be improved by training.

A common way to measure working memory is called the "n-back" task. Presented with a sequential series of items, the person taking the test has to report when the current item is identical to the item that was presented a certain number (n) of items ago in the series. For example, the test taker might see a sequence of letters like


presented one at a time. If the test is an easy 1-back task, she should press a button when she sees the second H and the second T. For a 3-back task, the right answers are K and N, since they are identical to items three places before them in the list. Most people find the 3-back condition to be challenging.

A recent paper reported (5) that training on a particularly fiendish version of the n-back task improves I.Q. scores. Instead of seeing a single series of items like the one above, test-takers saw two different sequences, one of single letters and one of spatial locations. They had to report n-back repetitions of both letters and locations, a task that required them to simultaneously keep track of both sequences. As the trainees got better, n was increased to make the task harder. If their performance dropped, the task was made easier until they recovered.

Each day, test-takers trained for 25 minutes. On the first day, the average participant could handle the 3-back condition. By the 19th day, average performance reached the 5-back level, and participants showed a four-point gain in their I.Q. scores.

The I.Q. improvement was larger in people who’d had more days of practice, suggesting that the effect was a direct result of training. People benefited across the board, regardless of their starting levels of working memory or I.Q. scores (though the results hint that those with lower I.Q.s may have shown larger gains). Simply practicing an I.Q. test can lead to some improvement on the test (6), but control subjects who took the same two I.Q. tests without training improved only slightly.

Since the gains accumulated over a period of weeks, training is likely to have drawn upon brain mechanisms for learning that can potentially outlast the training. But this is not certain. If continual practice is necessary to maintain I.Q. gains, then this finding looks like a laboratory curiosity. But if the gains last for months (or longer), working memory training may become as popular as and more effective than games like sudoku among people who worry about maintaining their cognitive abilities.

Now, some caveats. The results, though tantalizing, are not perfect. It would have been better to give the control group some other training not related to working memory, to show that the hard work of training did not simply motivate the experimental group to try harder on the second I.Q. test. The researchers did not test whether working memory training improved problem-solving tasks of the type that might occur in real life. Finally, they did not explore how much improvement would be seen with further training.


1. Flynn, J. R. 1987. Massive IQ gains in 14 nations: What IQ tests really measure. Psych. Bull. 101 (2) 171-191.

2. P.L. Ackerman (1987) Individual differences in skill learning: An integration of psychometric and information processing perspectives. Psychological Bulletin 102:3–27.

3. M.J. Kane, D.Z. Hambrick, and A.R.A. Conway (2005) Working memory capacity and fluid intelligence are strongly related constructs: comment on Ackerman, Beier, and Boyle (2005). Psychological Bulletin 131:66–71.

4. H.-M. Süss, K. Oberauer, W.W. Wittmann, O. Wilhelm, and R. Schulze (2002) Working-memory capacity explains reasoning ability—and a little bit more. Intelligence 30:261–288.

5. S.M. Jaeggi, M. Buschkuehl, J. Jonides, and W.J. Perrig (2008) Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences USA 105:6829-6833.

6. D.A. Bors, F. Vigneau (2003) The effect of practice on Raven’s Advanced Progressive Matrices. Learning and Individual Differences 13:291–312.

Monday, April 20, 2009

Visual Memory Has Astounding Capacity

My book on memory improvement presents much anecdotal evidence that people with outstanding memories use mental images of what they are trying to remember. Now, a formal scientific study validates the conclusion that ordinary humans have astounding memory capacity for visual (but not auditory) memories.

In this study, young adults (20-35 yrs) were shown a succession of object images, one every three seconds. They were told to remember as much as they could. After about each block of about 300 images, they were given a 5-minute rest break. After 10 such blocks (total images seen = 2,500; total time about 5.5 hours), they were tested with probe images and asked for each one if it had been seen before. Probe object images were paired in three ways: objects that were in a different category, the same category, or the same object but in a different state or pose. Performance accuracy was remarkably high for all conditions, respectively 92%, 88%, and 87% accuracy. Remembering 2,500 images with this level of recongition accuracy is truly astounding.

As comparison, a related study by another research group showed that auditory memory was markedly inferior. When subjects listened to sound clips (conversation, animal sounds, music, etc.) and then asked to distinguish new from old clips, under all conditions performance was systematically inferior to visual-memory performance.

Apparently, everyone has a degree of photographic memory. Certainly, the odds of recognizing that you have seen something are very high, at least under conditions where the image is a simple object. The storage capacity is huge. Does this apply to complex images that contain multiple details? Who knows for sure? The details can serve as useful cues or could even become confusing distractors. It is also not clear, if the visual-image capacity is limited to recognition or whether it applies to generating a recall without an image probe.

Even so, it is a good bet that memory performance will be optimized if memory items are converted to mental images.

Brady, T. F. 2009. Visual long-term memoryh has a massive storage capacity for object details. Proc. Natl. Acad. Sci. USA. 106: 6008-6010.

Cohen, M. A. et al. 2009. Auditory recognition memory is inferior to visual recognition memory. Proc. Natl. Acad. Sci. USA. 106 (14): 6008-6010.