Inability to filter and eliminate old information makes it harder to learn things as we age

Updated on: Saturday, January 12, 2013

It is the inability to filter and eliminate old information - rather than absorbing new stuff - that makes it harder to learn things as we age, a study has claimed.

Dr Joe Z Tsien, neuroscientist at the Medical College of Georgia at Georgia Regents University and Co-Director of the GRU Brain & Behavior Discovery Institute said, "When you are young, your brain is able to strengthen certain connections and weaken certain connections to make new memories."

It is this critical weakening that appears hampered in the older brain, according to the study. The NMDA receptor in the brain's hippocampus is like a switch for regulating learning and memory, working through subunits called NR2A and NR2B.

NR2B is expressed in higher percentages in children, enabling neurons to talk a fraction of a second longer; make stronger bonds, called synapses; and optimise learning and memory.

This formation of strong bonds is called long-term potentiation. The ratio shifts after puberty, so there is more NR2A and slightly reduced communication time between neurons.

When Tsien and his colleagues genetically modified mice that mimic the adult ratio - more NR2A, less NR2B - they were surprised to find the rodents were still good at making strong connections and short-term memories but had an impaired ability to weaken existing connections, called long-term depression, and to make new long-term memories as a result.

It's called information sculpting and adult ratios of NMDA receptor subunits don't appear to be very good at it, researchers said. "If you only make synapses stronger and never get rid of the noise or less useful information then it's a problem," said Tsien.

While each neuron averages 3,000 synapses, the relentless onslaught of information and experiences necessitates some selective whittling.

Insufficient sculpting, at least in the mouse, meant a reduced ability to remember things short-term - like the ticket number at a fast-food restaurant - and long-term - like remembering a favourite menu item at that restaurant. Both are impacted in Alzheimer's and age-related dementia.

The impaired ability could also help explain why adults can't learn a new language without their old accent and why older people tend to be more stuck in their ways, researchers said. The study was published in journal Scientific Reports.

Inability to filter and eliminate old information makes it harder to learn things as we age

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