12 noviembre, 2009


Conexiones entre dos neuronas.
IRB - 06-08-2009

Un trabajo en ratas demuestra que las neuronas nuevas borran los antiguos recuerdos para mantener la capacidad de aprendizaje
M.R.E. - Madrid io_cabecera= - 12/11/2009

Con la edad, la capacidad de recordar lo que se ha hecho el día anterior suele disminuir, hasta llegar a que, en muchos casos, no se recuerda lo que se ha dicho dos minutos antes, aunque se mantienen intactos recuerdos de muchos años atrás. Falla la memoria a corto plazo, que se ha demostrado que reside fundamentalmente en una parte del cerebro, el hipocampo. Según un trabajo realizado por un amplio equipo de investigadores japoneses en ratas y ratones, este fallo está relacionado con que no se borran los recuerdos antiguos, labor que hacen las neuronas nuevas, cuya generación puede disminuir con la edad, el estrés y los factores ambientales.

Cuando se transfieren los recuerdos a otra zona del cerebro, cambian
El ejercicio aumenta la neurogénesis

Es como si el disco duro cerebral estuviera lleno y fuera preciso formatearlo para permitir el almacenamiento de nuevos recuerdos. Este resultado sugiere que cuando no hay neurogénesis (generación de neuronas) se produce un fracaso de la memoria a corto plazo porque está literalmente llena. "Podemos tener problemas para adquirir nueva información porque la capacidad de almacenamiento está ocupada por recuerdos antiguos no borrados", explica Kaoru Inokuchi, que ha dirigido la investigación, publicada en la revista Cell.

Normalmente, según esta tesis, el nacimiento de nuevas neuronas promueve la pérdida gradual de recuerdos en el hipocampo y su transferencia a otros lugares del cerebro para integrarse en la memoria a largo plazo. Aunque el trabajo se ha hecho sólo con recuerdos relacionados con el miedo, Inokuchi cree que "todos los recuerdos que se almacenan inicialmente en el hipocampo resultan afectados por este mecanismo".

Se sabía que el hipocampo es uno de los pocos lugares del cerebro donde se generan nuevas neuronas en muchas especies de mamíferos, incluido el ser humano, incluso hasta edades avanzadas, pero no se sabía exactamente lo que hacen estas nuevas células cerebrales. El equipo japonés sospechaba que es precisa la integración de las nuevas neuronas para reforzar las conexiones neuronales, pero también pensó que su incorporación puede cambiar la estructura de la información preexistente, y eso es lo que ha confirmado en los experimentos.

En las ratas, se había comprobado en experimentos anteriores que el ejercicio físico da lugar a nuevas neuronas, lo que hace disminuir la dependencia de la memoria del hipocampo. "El aumento de la neurogénesis debido al ejercicio puede acelerar la destrucción de recuerdos en el hipocampo y al mismo tiempo facilitar la transferencia de los recuerdos al neocórtex. La capacidad de almacenamiento de recuerdos del hipocampo es limitada, pero de esta forma se puede aumentar la capacidad total del cerebro", explican los investigadores.

Con este estudio se sientan las bases para examinar la relación entre la neurogénesis y la capacidad de aprendizaje, añaden. Además, quieren ver cómo la transferencia de los recuerdos de una parte a otra del cerebro los cambia: pasan de ser muy ricos en detalle y en contexto a ser más genéricos.

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