domingo, 15 de noviembre de 2009

New Neurons Make Room for New Memories

New Neurons Make Room for New Memories

By Greg Miller
ScienceNOW Daily News
12 November 2009

The discovery that new neurons are born in the adult brain overturned decades-old dogma in neuroscience. But it also raised a host of questions about what exactly these neurons do (Science, 17 February 2006, p. 938). Now the authors of a new study suggest that the newcomers clear away the remnants of old memories to make room for new ones.

The brain's hippocampus is a bit like a secretary's inbox: Although many memories start out here, they eventually get filed to the neocortex for permanent storage. That's why the famous patient H.M., who had his hippocampus removed in experimental surgery for epilepsy, could remember events prior to his operation despite being unable to form any new memories afterward (Science, 26 June, p. 1634).

To investigate whether newly born neurons play a role in memory transfer to the neocortex, researchers led by Kaoru Inokuchi of the University of Toyama in Japan examined rats and mice with impaired hippocampal neurogenesis. The researchers trained the rodents to associate a particular chamber with a mild shock. Like normal animals, they remembered the association for weeks, freezing up any time they were placed in the chamber. This type of memory usually hangs out in the hippocampus for less than a month: When the researchers injected the brains of normal rodents with a drug that essentially turned off the hippocampus after 28 days, it had little to no effect on their freezing behavior--presumably because the memory had already moved on to the neocortex. But in the rats and mice with impaired neurogenesis, the same treatment substantially reduced freezing behavior, suggesting that the fearful memory had lingered longer than usual in the hippocampus instead of being transferred to the neocortex. A similar set of experiments with mice that exercised on a running wheel--an activity previously shown to boost neurogenesis--bolstered the idea that neurogenesis plays a role in transferring memories. In that case, memories appeared to shift from the hippocampus to the neocortex faster than usual.

Finally, recordings of neural activity indicated that that long-term potentiation, a physiological strengthening of neural connections thought to underlie this type of learning and memory, persists longer than usual in the hippocampus of the neurogenesis-impaired rodents. Altogether, the findings—reported tomorrow in Cell--suggest that new neurons act like an efficient secretary, making sure the physiological traces of old memories are promptly removed from the hippocampus inbox to make room for new ones.

"The authors went through a lot of experiments to prove their case," says Gerd Kempermann, an expert on neurogenesis at the Center for Regenerative Therapies Dresden in Germany. But Kempermann is not quite convinced that the specific job of new neurons is to clear the hippocampus for new information. An alternative explanation, he says, is that new neurons simply enable the hippocampus to work more quickly. "But their conclusion is certainly interesting and great food for thought."

martes, 10 de noviembre de 2009

The brain's anatomy of emotion induced by music

From Tranel, Adolphs, and collaborators, a fascinating piece of work reported in the International Journal of Psychology (check out the other articles in this issue, which has the theme 'Central and peripheral nervous system interactions: From mind to brain to body' Here is the abstract from their paper:

Does feeling an emotion require changes in autonomic responses, as William James proposed? Can feelings and autonomic responses be dissociated? Findings from cognitive neuroscience have identified brain structures that subserve feelings and autonomic response, including those induced by emotional music. In the study reported here, we explored whether feelings and autonomic responses can be dissociated by using music, a stimulus that has a strong capacity to induce emotional experiences. We tested two brain regions predicted to be differentially involved in autonomic responsivity (the ventromedial prefrontal cortex) and feeling (the right somatosensory cortex). Patients with damage to the ventromedial prefrontal cortex were impaired in their ability to generate skin-conductance responses to music, but generated normal judgments of their subjective feelings in response to music. Conversely, patients with damage to the right somatosensory cortex were impaired in their self-rated feelings in response to music, but generated normal skin-conductance responses to music. Control tasks suggested that neither impairment was due to basic defects in hearing the music or in cognitively recognizing the intended emotion of the music. The findings provide evidence for a double dissociation between feeling emotions and autonomic responses to emotions, in response to music stimuli.

I thought the music clips they used to elicit emotional responses were interesting.

By the way, here is another recent article by Salimpoor et al. on emotional arousal caused by music.