Tuesday, December 18, 2012

Primate Midlife Crisis

Increasingly, evolutionary psychologists have join with biologists to explore the relative universality of various phenomenon across the varied branches of the evolutionary tree.  An example of this was recently published in the Proceedings of the Academy of Sciences - USA.  In their study, investigators from several primate research centers across the globe joined forces to ask a simple question - Does it appear that various non-human primates experience a midlife crisis just as many humans do.  The answer they arrived at was  yes they do.

What evidence did they obtain that led them to arrive at this conclusion? First you should know what evidence is there that humans experience a midlife crisis.  When many people think of a midlife crisis they often imagine the middle-aged male whose behaviors may begin to resemble attempts to relive experiences that he had or had wished he had as a younger man.  Similarly, the behaviors of some middle-aged women in the midst of a crisis may also seem to be attempts to recapture their youth. Importantly, not every person may experience this midlife event or if they do, it may not manifest in the same way in every person.  Moreover, what most researchers consider a midlife crisis is much different that what is commonly portrayed in popular media.

What investigators have tended to focus upon as a hallmark of a personal crisis in midlife is a dip in subjective happiness or "well-being".  The data collected are from surveys that include such questions as:  How happy are you with your life?   and How stressful is your life?  An example of the typical pattern of results obtained from individuals of different ages is summarized below from a study by Stone et al. (2010).  Note the dip in overall assessment of subjective well-being (WB) expressed both by men and women during the 4th and 5th decades of life.  [My students might be more concerned about the precipitous decline in WB that appears to occur between the ages of 18 and 25!]

Compare the results above to those obtained for the WB or some of our close primate relatives in the graphs below from the recent paper by Weiss et al. (2012).

There appears to be a clear dip in their assessed WB between the ages of 20 and 40.  But perhaps it would be wise to delve a litter further into the details of the study before we accept that our primate relatives experience a midlife-crisis.

First, your probably thinking it unlikely that the data Weiss et al. obtained was based upon  questionnaires completed by the primates.  Indeed, the assessments of WB were subjective, but they were assessments that were made by humans who were most familiar with the individual animals included in the study.  The raters were zoo keepers, volunteers, researchers, and caretakers who knew the animals for 2 years or more. These humans answered a 4-item survey in which they judged the animals mood (+ vs -), how pleasurable the animal experiences in social interactions, how successfully the animal was at achieving its goals, and how happy the human would be if they were the subject for a week. 

So the data from which the conclusions of the study are drawn are human assessments of the subjective WB of the animal and includes an item that required the human making the assessment to imagine themselves to be the primate they were assessing.  This got me thinking.....

1) How well is any human, even one familiar with primates, accurately able to assess the subjective WB of another human, let alone the WB of a primate?

2) The raters obviously know how old the primates they rated were.  Might  that knowledge play a role in determining their assessments of WB?

Would you consider these significant limitations of the study? Please feel free to share your thoughts.

What I found most interesting about the study was the discussion in which the authors review some of the theories for why there is a "U" shaped age-related pattern to subjective WB in humans.

"The midlife dip cannot be explained by the effects of having young children in the household, and it is similar in males and females, so is not likely connected to menopausal changes or to societal sex roles. A selection explanation, because of the greater longevity of happy people, is likewise unable to account for the midlife dip. One socioeconomic theory is that the U shape reflects hedonic adaptation in which impossible aspirations are first painfully felt around midlife and then slowly and beneficially given up. Another theory is that the curve is linked to financial hardship and thus likely to be less pronounced in those older individuals with higher resources. A third theory is that human aging may bring with it the ability to experience less regret. In short, there is little convergence of explanations about the U-shapes origins." (p. 19949)

In their discussion the authors do suggest that happiness may contribute to longevity and that this may account for the upswing in WB the primate populations they studied.  They also suggest that elevated WB may be adaptive to individuals in their early and later years or that elevated subjective WB may be somehow maladaptive during midlife.

It may also be helpful to consider the individual frame of reference for assessing subjective WB, whether the individual is human or a social primate.  In midlife comparisons may be made both retrospectively and prospectively - against what life had been like when younger and what it could be as compared to others of a similar age group as well as to elders.  Perhaps from this perspective subjective well being is less than desirable.  By contrast as a youth prospects may appear to be quite good and at an advanced age WB may be judged chiefly from what has been accomplished across a lifetime (this seems similar to the socioeconomic theory mentioned above.) In either case subjective WB may be enhanced.

From a neuroscience perspective the authors mention that the age-related "U" shaped pattern of WB may be attributed to maturational changes that occur in various  regions of the brain.  As an example, they site a 2004 study by Urry et al. that compared age correlated age  related difference in WB with activation patterns in the frontal lobes of the brain. They found that enhanced activation of the frontal lobe in the left hemisphere was positively correlated with positive subjective WB (Note: The range of ages of their participants.was between 57 and 60 years).  Left unanswered is if a similar result would also be found among participants in older and younger cohorts.

So at least at my age things appear to be looking up with regard to my subjective WB  ; )


Tuesday, December 4, 2012

Is the Quality of an Orchestra's Performance Attributable to Mirror Neurons?

Members of a orchestra in the midst of a performance of a symphony by any of your favorite composers must all be attuned to the instrumentation of other performers as well as their own contributions.  For example they must anticipate their own upcoming parts as well as those of the other performers.  The conductor's role in helping keep all the musicians in sync is highly regarded by some, but questioned by others. Couldn't the orchestra perform just as well without a conductor?  Alternatively, should the conductor deserve most of the credited for the distinctive character of what have been the most highly regarded orchestras?   Perhaps both the orchestra members and the conductor deserve equal credit for their most exceptional performances. What, if any information can neuroscientists contribute  that might help answer these questions? 

A report on NPR may be of interest.  In the recent segment, Do Orchestras Really Need a Conductor?, Shankar Vedantam  interviewed Yiannis Aloimonos from the University of Maryland to learn what he and his colleagues found when they conducted experiments to learn what the conductor contributes to the performance of the orchestra. 

In a study, published in the open access journal PlosOne, the investigators were able to map the degree to which the orchestra and conductor were in sync via sensors placed on the ends of the violinist's bows and the conductor's wand.  They asked two different conductors to lead the same orchestra in five different pieces (* see my note at the bottom of this post).  In addition to the data they obtained from the sensors,  they asked experts to judged the subjective quality of the performances.

The statistical analysis of the data obtained from the sensors is complicated, but essentially it allowed the investigators to assess just how well in sync the musicians and conductor were as well as how much "control", "influence" or "drive" the conductor had on the musician's performance.

Here is the briefest of summaries of the outcome:
(Asterisks indicate statistically significant differences between C1 and C2)
  • The two conductors exhibited different degrees of influence over the orchestra (C1 > C2)
  • Under one conductor (C2), the musicians appear to have had a greater influence on each other while playing 3 of 5 pieces.  
  • In 2 of the 5 pieces that the orchestra played, the subjective quality of the performance differed depending upon the conductor; in one instance the price led by conductor 1 prevailed and in the other the performance of the other conductor was judged to be better.
The authors conclude that "... appreciation of (the) music orchestras’ performance was associated to the concurrent increase of conductor-to-musician influence and a reduction of musician-to-musician information flow. " (p. e35757).

In other words, the conductor does have an influence on the aesthetic quality of the performance as long as her/his contributions  "drive" the performance of the orchestra and that the relative influence of other musicians on each other's performance is secondary to that of the conductor's.  

Examine the graphs above and below carefully.  Do they appear to support the authors' conclusions? 

(Asterisks indicate statistically significant differences between C1 and C2)

Statistically the there appears to be a significant difference in the drive exerted on the orchestra by the two conductors during performance of pieces 3 and 5 (C1 > C2) and likewise, musician-to-musician influence was greater during performance of pieces 1, 2, and 3 under the direction of C2.  Differences in subjective aesthetic perception of the performances were significant for piece 3 and 5.  In both instances, C1 was able to exert a greater influence on the musicians. However in one instance the subjective ratings of the performance under direction by C1 were better (Piece 3) and in the other instance the performance under the direction of C1 were judged to be poorer. Obviously there seems to be some complex interaction of factors that is occurring.  

What the authors of the paper argue is that in the instance of Piece 3, the relatively greater degree of direction achieved by C1 in combination with diminished musician-to-musician influences resulted in a more aesthetic performance than what was achieve by C2.

So far so good.  But what explains the poorer performance of Piece 5 under the direction of C1, despite achieving relatively greater drive than C2?  The authors argue that despite exerting greater drive, C1 did not decrease the musician-to-musician influences any more than C2.

Altogether, this pattern of results supports the conclusions of the researchers.

But might there be more at play here?  Is it possible that the piece itself may also play a role in whether the drive achieved by the conductor  in combination with relatively less musician-to-musician is ultimately what results in an aesthetically pleasing performance? The authors admit as much, but future research will be needed to assess the influence of the musical score itself.

Why might any of this interest a neuroscientist, even those neuroscientists who do not regularly attend orchestral performances?

What might be going on in the brain of the musicians and the conductor that interests a neuroscientist?   Although it is highly speculative, the authors of the paper suggest that  the interaction between conductor and the orchestra.

Mirror neurons are neurons that are activated when an individual engages in a specific action or observes another individual engage in that same action.   Mirror neurons were first identified by researchers recording from individual neurons within the brain's of monkeys (the goal of this work was to determine if with training, the monkeys could remotely control the movement of a prosthetic arm and hand using only the input from these neurons). However subsequent neuro-imaging studies with humans have identifies networks with some brain regions that appear to function similarly to mirror neurons.

Presumably the conductor's influence on the members of the orchestra may be mediated by networks comprised of mirror neurons. It also seems likely that  the musician-to-musician interactions might be mediated by such networks. What may matter aesthetically to the audience is that the influence of the conductor dominates. 

What is true for the orchestra may also be true for the chorus! Let me know what you think!

In a study published in the journal Science in 2002 the investigators demonstrated that some mirror neurons of monkeys responded most strongly to the the sight of actions paired with the sounds that the actions caused (i.e., paper being ripped, a stick being dropped).  Might this be comparable to the gestures of the conductor and the resulting changes in the musical passage that they are intended to signal?  I was also reminded of a study published in the journal Nature a few years ago in which neuroscientists studying the neural circuits that control the songs of some birds report evidence of mirror-neuron-like activation of the song system when the birds are exposed to the characteristic songs of their own species, but not distinctive songs of a another species of songbird.  These studies were supposedly the first to find evidence of mirror neuron networks in a non-primate species.

Mirror neurons have received a great deal of attention over the past decade. They have been implicated as serving a role in observational learning and in empathic perception.  One theory that has garnered a great deal of interest is that autistic individuals may have deficits in the mirror neuron circuitry.

NOTE:  In actuality the study did not employ an entire orchestra, only 8 violinists.   It is also not clear specifically what musical pieces were used, although the authors mention Mozart Symphony No. 40

  • D'Ausilio A, Badino L, Li Y, Tokay S, Craighero L, et al. (2012) Leadership in orchestra emerges from the causal relationships of movement kinematics. PLoS ONE 7(5): e35757. doi:10.1371/journal.pone.0035757
  • Iacoboni M, Molnar-Szakacs I, Gallese V, Buccino G, Mazziotta JC, et al. (2005) Grasping the intentions of others with one’s own mirror neuron system. PLoS Biol 3(3): e79.
  • Kohler, E., et al. (2002).  Hearing sounds, understanding actions: Action representation in mirror neurons. Science, 297, 846-848.
  • Miller, G. (2008). Mirror neurons may help songbirds stay in tune.  Science, 319, 269.
  • Ramachandran, V.S. & Oberman, L.M. (November, 2006).  Broken mirrors. A theory of autisms.  Scientific American, 295 (6), 63-69.
  • Rizzolantti, G., Fogassi, L., & Gallese, V. (November, 2006).  Mirrors in the minds.  Scientific American, 295 (6), 54-61.