Older mice with a full set of teeth were only slightly slower. However, old mice whose molars had been removed were unable to remember how to find the platform, and consistently headed off in the wrong direction. Examination of the hippocampus showed that vital cells called glia had worsened far more than usual. Cambridge Dr Onozuka's team followed by their research by using magnetic imaging to scan brain activity while people chewed. They found that there was a big increase in hippocampal signals during this activity.
Nobody knows why chewing stimulates the mind.
However, Dr Joyce Wau, a specialist in ageing at the Molecular Medicine Centre at Edinburgh University, postulates that chewing sends a signal to the hippocampus which in turn eases levels of stress hormones in the blood. If older people chew less, their stress levels might rise enough to cause a decline in short-term memory. Dr Felicia Huppert, an expert in memory and ageing at Addenbrooke's Hospital, Cambridge, was sceptical of the results, and warned that the results of neuro-imaging had to be interpreted very carefully. Dr Huppert's colleague Professor Joe Herbert, an expert in anatomy, said it had been shown that stress damaged the hippocampus. However, he had not heard of any link to chewing.