• Question: I just read an article (https://goo.gl/JrK5yY) that says neurons do not grow past early adolescence. It does say that its perhaps connections that are more important anyway, but what is the understanding about learning as we get older? Is it inevitably more difficult and - if so - how can we compensate to work smarter?

    Asked by Abena to Sveta, Matt, Lucía, Lorna, Kathryn, Jacob, Iroise, Emma, Courtenay, Camilla on 27 Mar 2018.
    • Photo: Emma Meaburn

      Emma Meaburn answered on 27 Mar 2018:

      Hi there. Great question, and somewhat tricky for me to answer — I had to turn to Iroise Dumontheil (@Iroise) to help me fully answer your question! Neurons don’t grow past adolescence, but connections between them (synapses) get created and removed throughout development. There are critical periods of more activity though, with early infancy being a period of synapse creation (synaptogenesis), and adolescence being a period of synaptic removal (synaptic pruning). This is off-topic, but some disorders that typically emerge in early adulthood (such as Schizophrenia) are thought in part to be due to over active synaptic pruning during adolescence.

      In terms of learning, practise improves performance regardless of age.

    • Photo: Lucía Magis Weinberg

      Lucía Magis Weinberg answered on 30 Mar 2018:

      Hi! We have increasing evidence that networks of neurons, including both the structural connections between them, as well, as shared patterns of firing activity, are key for behaviour, including learning. As Emma Meaburn pointed out, one important structural change in adolescence is the strengthening of connections that already exist. Longer-range connections between brain regions get more and more myelinated (covered in a fatty substance that improves transmission of signals in the cells). A new area of research is now describing the architecture of these networks. It seems that during adolescence, the brain networks become increasingly segregated into more distinct modules. So to recap, there are many other mechanisms supporting learning and other processes beyond the need for new neurons.

      For some abilites, but not all, aging can make things a bit more difficult. There are certainly aspects in which older individuals will perform better than younger participants, as they have more experience to draw from. In general, we have strong evidence that physical health plays a key role in brain health: aerobic and anaerobic exercise is an important protective factor at all ages.

    • Photo: Sveta Mayer

      Sveta Mayer answered on 17 Jun 2018:

      Hi Abena, for me your question flags up several considerations we’d make in developmental neuroscience. So have aimed to share some of my reflections in hope to answer your queries.

      As Emma and Laura mention there is synaptogenesis and pruning as well as development with age. There is also neuronogenesis and plasticity and the influence of this through individual differences from the time of conception and across the lifespan.

      The paper you refer to (https://goo.gl/JrK5yY) refers to research on neuronogenesis. In the paper researchers were reporting on findings of hippocampal neuronogenesis using immunohistochemistry techniques to detect what type of brain cells (neurones or glial) are generated from precursor cells, how many are generated and at what age. Thinking about the findings from this paper, I noted the small sample size (which isn’t unusual) and found it interesting that in one sample neuronogenesis was reported. This is interesting because neuronogenesis is influenced by genetic inheritance before birth and then epigenetics i.e. gene activation/deactivation is dependent upon the child’s experiences.

      Why is this interesting? Well, I wondered does neurogenesis arise in adulthood in some people and not others, if so what influences this and for how long? As this research continues, meta-analysis of several research studies with small sample size, such as the one you refer to undertaken to compare and contrasted the research studies will reveal more about our understanding of human neuronogenesis. The validity of meta-analysis will of course be dependent upon how far the research studies and the samples they draw upon are comparable.

      Your insight about the value of focusing upon synaptic plasticity (changes in connections between neurons) when thinking about learning is sound. These changes may be to strengthen or diminish connections. Synaptic plasticity arises from point of neurogenesis, neuron differentiation and migration away from the site of neurogenesis so the paper you cite doesn’t refer to this. Given your question also asks about learning as we get older, you might find reading the review paper cited below (Power & Schlaggar, 2017) which refers to seminal work by Hebb, 1949 about activity dependent synapse plasticity (if you’ve not as yet familiar with this). Hebb, in his work considered what we often refer to as: “neurones that fire together, wire together”. So in developmental cognitive neuroscience this may be considered as development of ‘memory’ networks.

      In response to your query about learning as we get older, there are several schools of thought informing this. I’ll refer to one that resonates with me and my thinking: the interactive specialisation approach – from birth and as we get older we draw upon several brain networks to acquire the skills and behaviour being learned but the brain remains responsive to learning through the lifespan. This means even if a given skill and behaviour is learned, the brain still has capacity to learn other skills and behaviours or unlearn these. However, time to develop expertise is needed so learning new skill and behaviours earlier in life enables development of expertise but this doesn’t mean we cannot learn as we get older, it just means we still need time to develop the expertise.

      Reference: Power, J.D. & Schlaggar, B.L. (2017). Neural plasticity across the lifespan. WIREs Dev Biol 2017, 6:e216. doi: 10.1002/wdev.216