Human brain produces new cells until at least age 90, Spanish researchers find

According to the Severo Ochoa Molecular Biology Centre, part of Madrid Autonomous University and the High Council for Scientific Research (CSIC), adult brains not affected with degenerative conditions such as Alzheimer’s carry on creating new neurons until around the age of 90, replacing those which die off.

This process, known as Adult Hippocampal Neurogenesis, is impeded by the present of Alzheimer’s.

Neuron regeneration slows with age – and earlier studies have revealed that age-related memory loss begins to set in at around 27 years old – but does not stop altogether, which explains why it is still possible for the middle-aged and even elderly to learn new mental and physical skills.

Published in the magazine Nature Medicine, the Severo Ochoa Centre’s report says: “Despite a slight reduction in the number of neurons generated during ageing, a high number of these neurons remain present in individuals who do not suffer from any neurological illness until at least the age of 87.”

The investigation analysed Adult Hippocampal Neurogenesis by studying and comparing 13 individuals with healthy brains and 45 diagnosed with Alzheimer’s, and found that the number of new neurons dropped dramatically in the early stages of the disease, before continuing to decline more gradually as the condition advanced.

This explains why the initial onset of Alzheimer’s is more marked, but its progress often appears to slow down over the years.

The study shows these cells, in Alzheimer’s patients, encounter problems at different stages of their process of maturing, meaning the number of neurons that develop in full is lower than the total in non-sufferers.

Early detection of reduction in new neuron generation could serve as a warning flag that a person may go on to develop Alzheimer’s, the report states.

Additionally, if a method was found to increase the ‘birth’ and full development to maturity of new neurons in humans, this could lead to treatments that allowed Alzheimer’s to be considerably reduced, or its process slowed down.

The team has already successfully ‘grown’ new neurons to full maturity in laboratory mice, but has not yet reached the stage of being able to try the process in human beings.

Humans are thought to have around 100 billion neurons in the brain and a billion in the spinal cord, and all of these play different roles in helping the body, its organs, glands, muscles and all five senses function.

Neurons are ‘messengers’ that send information to and from the brain, and between each other within the brain, via electrical impulses transported from one to another by chemicals, known as ‘neurotransmitters’ – a process discovered by Spanish neurologist Santiago Ramón y Cajal in the late 19^th century.

Cells damaged by trauma or destroyed through ageing can never be replaced, but their axons, or the strands between each end, sometimes do adapt – new ones can sprout from damaged ones to create extra connections within neurons, or those axons which play a similar role to damaged ones can become aroused to higher levels to compensate.

This adaptation is known as ‘brain plasticity’, which helps to retain or recover lost functions in some cases, including memory.

Scientists have discovered in recent years that the process of plasticity continues from birth until death, irrespective of age.