01 November 2002
The Lancet Neurology, Volume 1, Number 7
The idea that the adult brain is resistant to adaptation, learning, and neurorehabilitation may have to be rethought after a demonstration of plasticity in the brains of adult owls that is comparable to that seen in young animals.
Young animals, whether birds or human beings, have long been known to acquire new skills and adapt to change better than adults; this is also true in cases of brain damage, from which children tend to recover faster and better than adults. However, “in older animals, plasticity can be dramatically increased when learning tasks are broken down into small steps” says Brie Linkenhoker of Stanford University, California, USA,, lead author of a recent paper (Nature 2002; 419: 293–96).
Barn owls have a mental map that aligns the auditory and visual worlds to help them locate prey. By applying prismatic spectacles to the birds Linkenhoker and coauthor Eric Knudsen could shift the visual map out of alignment with the auditory map. Young owls were able to quickly adapt elements of the auditory map, such as the interaural time difference (ITD), to fit in with the shifted visual map, even when large changes were suddenly made. When the researchers shifted the visual map by 23° the juvenile owls adapted their ITD by 43 ?s in a few months. Adults, however, achieved only a 4 ?s correction to their ITD in twice the length time.
“It may be adaptive for younger animals to be more plastic and to learn quickly”, Linkenhoker explains “whereas it may be more adaptive for the brains of older animals to be more predictable and more reliable.”
The researchers then tried to re-train adult owls to a 17° shift in the visual map. Owls in the single-step group were given 17° prismatic spectacles and another group had their visual map shifted in gradual steps from 6° to 11°, and finally to 17°. In the first of the small steps the adult owls adjusted their ITD more in a few weeks than those subjected to a single large step did in months.
This retraining of adult brains in increments suggests how neurorehabilitation in human adults with brain damage from stroke or trauma may be tailored to achieve better recovery.
Once the spectacles were removed from the owls the ITD returned to normal. This shows a possible increase in the capacity for adaptive change that could have implications for the treatment of brain-damaged patients.
“How this relates to the damaged adult brain is less clear, as the animals
were healthy. Nonetheless, the fact that the adult brain may have the potential
for ‘metaplasticity’ is intriguing and bodes well for the future of neurorehabilitation”,
says Shaheen Hamdy of The University of Manchester, UK.
© Copyright 2002, The Lancet