Cabbies’ brains

The BBC has a nice piece covering the continuing research of Prof. Eleanor Maguire (Wellcome Institute of Neurology, University College London) on the distinctive development of the hippocampus in the brains of London taxi drivers: Taxi drivers’ brains ‘grow’ on the job. Prof. Maguire’s research in this area is pretty extensive (see publication list). She’s found a great naturally occurring experiment in the brains of cabbies who have to navigate London’s notoriously byzantine downtown streets.

As the BBC report describes, driving a cab in London is difficult and demands a well-developed knowledge of urban geography:

In order to drive a traditional black cab in London drivers have to gain “the knowledge” – an intimate acquaintance with the myriad of streets in a six-mile radius of Charing Cross.

It can take around three years of hard training, and three-quarters of those who embark on the course drop out, according to Malcolm Linskey, manager of London taxi school Knowledge Point. “There are 400 prescribed runs which you can be examined on but in reality, you can be asked to join any two points,” he told BBC News Online.

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Cultural Aspects of PTSD, Part II: Narrative and Healing

Bremner et al. 2000.  MRI showing decreased hippocampal volume in Vietnam veterans diagnosed with PTSD.

Narrative and memory are interwoven in our consciousness, and thus explorations into trauma from both humanities and social science perspectives almost invariably discuss narrative in one form or another. An ongoing debate within psychological research, for example, ponders whether the coherence of trauma stories is correlated to the amount of emotional distress associated with a given traumatic memory. It is hypothesized that the greater the distress, the less organized the narrative. If this were the case, we might expect that the coherence with which an individual is able to talk about the trauma would increase as the memory is processed and resolved, a finding for which we have some evidence.

We do know – when it comes to Post-Traumatic Stress Disorder (PTSD) – that narrative matters. As I wrote in an earlier post, the most effective therapies yet proven for reducing PTSD symptoms are the exposure therapies, particularly Prolonged Exposure (PE) therapy. These therapies are more effective for reducing the full range of PTSD symptoms than any pharmaceutical yet identified. And the crux of these therapies rests on telling the story of the trauma, sometimes over and over again. This simple practice, this process of speaking, has been reliably demonstrated to result in an improvement of PTSD symptoms for many patients.

But for all its clinical benefit, this extraordinary observation tells us very little about the mechanisms of psychic healing after trauma. Instead, it points to a growing body of evidence that suggests it is not just narrative that matters in PTSD, but, more intriguingly, that it is the type of narrative that matters. Unstructured psychodynamic therapies, for example, have not been demonstrated to lessen the severity of PTSD, even among patients who continue in therapy for years. And yet certain ways of narrating memory do make a difference, and this phenomenon once again points to a role for anthropologists and other culturally-minded researchers in exploring the cultural-emotional-physiological-environmental interactions at play in post-traumatic processing.

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Monkeys and robots teaming up — worried?

As Daniel discussed in January in Monkey Makes Robot Walk!, a number of researchers are working on brain-machine interfaces by attaching prostheses to monkeys. Science Daily carries a new story, Mind Over Matter: Monkey Feeds Itself Using Its Brain, about a University of Pittsburgh School of Medicine experiment in which a monkey successfully used a human-like prosthetic limb to feed itself. As the Science Daily story reports:

Using this technology, monkeys in the Schwartz lab are able to move a robotic arm to feed themselves marshmallows and chunks of fruit while their own arms are restrained. Computer software interprets signals picked up by probes the width of a human hair. The probes are inserted into neuronal pathways in the monkey’s motor cortex, a brain region where voluntary movement originates as electrical impulses. The neurons’ collective activity is then evaluated using software programmed with a mathematic algorithm and then sent to the arm, which carries out the actions the monkey intended to perform with its own limb. Movements are fluid and natural, and evidence shows that the monkeys come to regard the robotic device as part of their own bodies.

According to the team, this is the ‘first’ example of the ‘use of cortical signals to control a multi-jointed prosthetic device for direct real-time interaction with the physical environment (’embodiment’)’ (from the abstract to the Nature article) (I’m always dubious about such ‘firsts,’ especially as this team has been announcing work on this project since at least 2004; but the research is still fascinating even if not a ‘first’).

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Rats’ visual systems made plastic by anti-depressants

Blogging on Peer-Reviewed ResearchMy mind raced for potential titles to a post when I read the recent report from Science, ‘The Antidepressant Fluoxetine Restores Plasticity in the Adult Visual Cortex,’ by a team headed by José Fernando Maya Vetencourt (abstract), but I’ve opted to be demure, rather than go with some of my other options (like ‘Anti-depressants the “Cocoon” pool for brain?’ or something similarly outrageous).

The research team investigated wither fluoxetine, a selective serotonin reuptake inhibitor (SSRI), could restore plasticity in the visual system of adult rats. They chose fluoxetine because long-term regimens of the drug promote neurogenesis and synaptogenesis in the hippocampus and increased activity of neurotrophin brain-derived neurotrophic factor (BDNF) and its primary receptor, TrkB (close paraphrase to the original article). These effects have been shown essential to the drug’s effect; block one of these processes, and the anti-depressant doesn’t work nearly as well. In order to test plasticity, the team studied how rats responded to monocular deprivation — covering one eye — both the initial shift in ocular dominance and then the recovery of visual function after long-term monocular deprivation. In general, the fluoxetine-treated rats responded in exaggerated fashion to both conditions, suggesting that plasticity was greater with long-term administration of the drug. From the abstract:

We found that chronic administration of fluoxetine reinstates ocular dominance plasticity in adulthood and promotes the recovery of visual functions in adult amblyopic animals, as tested electrophysiologically and behaviorally. These effects were accompanied by reduced intracortical inhibition and increased expression of brain-derived neurotrophic factor in the visual cortex. Cortical administration of diazepam prevented the effects induced by fluoxetine, indicating that the reduction of intracortical inhibition promotes visual cortical plasticity in the adult. Our results suggest a potential clinical application for fluoxetine in amblyopia as well as new mechanisms for the therapeutic effects of antidepressants and for the pathophysiology of mood disorders.

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Doidge on The Brain That Changes Itself

Dr. Norman Doidge has a short column on his own book, The Brain That Changes Itself, over at Science Blog. His book is extremely good, but it’s funny, when you read the column, it sounds like a science ‘travel log,’ as if he went on a long brain science roadtrip. It seems to be a leitmotif in a lot of recent popular science book; traveling around, meeting scientists, having a bit of a chat, getting a bit of personal back story as well as a chance to talk about their research. Or am I the only one who feels this way?

One of the commenters on the Science Blog says something about a book of ‘anecdotal evidence,’ which I think is pretty ignorant. Anyone who regularly reads neuropathology knows that ‘anecdotal evidence’ of human brain injury is not just typical, it’s essential. Singular cases can have an enormous impact on our knowledge of how the brain works by causing such distinctive disruptions of function. Where would we be in brain sciences with Phineas Gage, the folks Oliver Sachs writes about, and this unlucky brotherhood?

Check out Doidge’s column — and his book gets a strong recommendation as well.

Smell, fear and sensory learning

Blogging on Peer-Reviewed ResearchWen Li, James D. Howard, Todd B. Parrish, and Jay A. Gottfried have a fascinating article in the most recent edition of Science, ‘Aversive Learning Enhances Perceptual and Cortical Discrimination of Indiscriminable Odor Cues.’ The researchers trained subjects to discern between the aroma of chemicals that initially were indistinguishable using electric shocks (!) coupled with one of the two aromas. The research is a great example of perceptual learning, a form of neural enculturation that I think is absolutely essential to understanding cultural difference but little appreciated in anthropology.

Subjects in the experiment were given a test of their ability to discern between very closely related chemicals: ‘On each trial, subjects smelled sets of three bottles (two containing one odorant, the third containing its chiral opposite) and selected the odd stimulus.’ Before the training, subjects selected the odd odor out 33% of the time — no better than random. After the repeated association of one chemical with shocks, subjects’ ability to discriminate the smells improved markedly, showing that negative reinforcement training could ‘enhance perceptual discriminability between initially indistinguishable odors.’ Moreover, the neural representation of the smells changed, as found with fMRI.

From their abstract:

We combined multivariate functional magnetic resonance imaging with olfactory psychophysics to show that initially indistinguishable odor enantiomers (mirror-image molecules) become discriminable after aversive conditioning, paralleling the spatial divergence of ensemble activity patterns in primary olfactory (piriform) cortex. Our findings indicate that aversive learning induces piriform plasticity with corresponding gains in odor enantiomer discrimination, underscoring the capacity of fear conditioning to update perceptual representation of predictive cues, over and above its well-recognized role in the acquisition of conditioned responses. That completely indiscriminable sensations can be transformed into discriminable percepts further accentuates the potency of associative learning to enhance sensory cue perception and support adaptive behavior.

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