Category: Brain Mechanisms

Visual Rewards

Blogging on Peer-Reviewed ResearchWhy will we study a favored painting again and again?  Or gaze on our lover’s face with such pleasure, even after years and lines have mounted?

 I came across an article, “Perceptual Pleasure and the Brain,” by Irving Biederman and Edward Vessel in American Scientist.  They studied the distribution of mu-opioid receptors, associated with the modulation of pleasure and pain, in the visual cortex.  Their basic result: “The receptors are sparsest in the early stages of this [central visual] pathway, the so-called V1 to V4 areas, where an image is processed as local bits of contour, color and texture.  Intermediate stages of visual processing, such as the lateral occipital area and ventral occipito-temporal cortex, which integrate local information to detect surfaces, objects, faces and places, contain greater number of opioid receptors.  The receptors are densest in the later stages of recognition, in the parahippocampal cortex and rhinal cortex, where visual information engages our memories.”

 Thus, they argue, “a visual stimulus that elicits many episodic or semantic memories should be more pleasing (or more interesting) than a stimulus that brings forth fewer mental associations.” 

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Mice brains on stress

Blogging on Peer-Reviewed ResearchIn February 2006, a research team at University of Texas and Tufts University published a piece in Science on how experience could modify the structures in the brain that affect the production of dopamine through brain-derived neurotrophic factor (BDNF) (abstract here). The research team used ‘social defeat’ to explore ‘the neurobiological mechanisms through which psychosocial experience alters the activity of the mesolimbic dopamine pathway’; in other words, the malleable system that can induce structural changes in the brains of mice in response to persistent patterns of social interaction.The abstract, while a little thick, suggests all sorts of intriguing possibilities:

Mice experiencing repeated aggression develop a long-lasting aversion to social contact, which can be normalized by chronic, but not acute, administration of antidepressant. Using viral-mediated, mesolimbic dopamine pathway–specific knockdown of brain-derived neurotrophic factor (BDNF), we showed that BDNF is required for the development of this experience-dependent social aversion. Gene profiling in the nucleus accumbens indicates that local knockdown of BDNF obliterates most of the effects of repeated aggression on gene expression within this circuit, with similar effects being produced by chronic treatment with antidepressant. These results establish an essential role for BDNF in mediating long-term neural and behavioral plasticity in response to aversive social experiences.  

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Autism and Mirror Neurons

Autism has been my latest lens for learning about neuroanthropology. It started with reading claims that autism is linked to mirror neuron disfunction. Mirror neurons are currently used to explain how the brain understands the intentions and emotions of others. Researchers suggest that lack of brain activity in mirroring areas of the brain found in autistic children could explain deficits in social interaction and empathy. A related article on the site links the mirror system to the study of culture: Culture Influences Brain Cells: Brain’s Mirror Neurons Swayed By Ethnicity And Culture. A study compared reactions of subjects to both American and Nicaraguan hand gestures, measuring differences in mirror neuron activity in the brain depending on who was giving the information and whether they were a member of their own ethnic group or a different group.

“We believe these are some of the first data to show neurobiological responses to culture-specific stimuli,” said Molnar-Szakacs. “Our data show that both ethnicity and culture interact to influence activity in the brain, specifically within the mirror neuron network involved in social communication and interaction… An important conclusion from these results is that culture has a measurable influence on our brain and, as a result, our behavior. ” “We are the heirs of communal but local traditions,” said Iacoboni. “Mirror neurons are the brain cells that help us in shaping our own culture. However, the neural mechanisms of mirroring that shape our assimilation of local traditions could also reveal other cultures, as long as such cross-cultural encounters are truly possible. All in all, our research suggests that with mirror neurons our brain mirrors people, not simply actions.”

I’m still trying to wrap my mind around this article—it seems as if it would be a given that culture impacts behavior so am not sure if they discovered something new so much as found a more scientific way of measuring it. Could this possibly be a tool that would indicate whether someone would suffer from culture shock? And linking it back to the first article, would this imply that autistic people would have equal trouble picking up on social cues regardless of who they are with while for others it would depend on whether they share the same cultural background?

Mirror effects in neurons learned?

Blogging on Peer-Reviewed ResearchLike many observers of the neurosciences from other fields, I have watched the debate about the function, origin, and nature of ‘mirror neurons’ with no small amount of interest. Since their discovery in the early 1990s by Giancomo Rizzolatti and his research group at the University of Parma, the ‘mirror system(s?)’ in primates and humans have been extensively explored and discussed.

For anyone living under a neurosciences rock, ‘mirror neurons’ are typically premotor or parietal neurons that are active both when a subject perceives and executes an action. In a host of research projects which I’ll probably try to discuss later (I wrote a lengthy piece on them that was recently rejected by a major anthro publication, and I’m considering posting the original in the anthropology open source archive and then doing a MAJOR revision to seek publication elsewhere). Anyway, mirror neurons have been linked to action understanding, empathy, imitation (a personal interest), language, and ‘mind reading’ (not a sixth sense, but the abiltity to understand other’s intentions and perceptions).

A new paper by Caroline Catmur, Vincent Walsh, and Cecilia Heyes (one of the really innovative scholars working on mirror neuron research) in Current Biology has some fascinating implications for neuroanthropology(abstract or pdf download). In particular, the article suggests, in the words used in the abstract:

…it is unclear how mirror neurons acquire their mirror properties—how they derive the information necessary to match observed with executed actions. We address this by showing that it is possible to manipulate the selectivity of the human mirror system, and thereby make it operate as a countermirror system, by giving participants training to perform one action while observing another. Before this training, participants showed event-related muscle-specific responses to transcranial magnetic stimulation over motor cortex during observation of little- and index-finger movements. After training, this normal mirror effect was reversed. These results indicate that the mirror properties of the mirror system are neither wholly innate nor fixed once acquired; instead they develop through sensorimotor learning. Our findings indicate that the human mirror system is, to some extent, both a product and a process of social interaction [please note I’ve removed citation numbers that appear in the abstract].

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