We are often told that the best time to learn a new language is when we are young. It’s also true that as we age, we lose some cognitive ability. But the idea that we reach some point at which further learning is no longer possible is incorrect. It all comes down to something called neurogenesis, and it applies to both us and our dogs.
What is neurogenesis?
Neurogenesis is the process by which neurons are formed in the brain. Neurons are the fundamental units of the brain and nervous system – they transmit information around the body to other nerve cells, muscles and even gland cells. Most neurons have a cell body, an axon, and dendrites. In a nutshell, neurons are crucial to coordinate all the necessary functions of life. Historically, neurogenesis was thought to only occur in developing organisms like babies or puppies, and that we stop producing new neurons as we age. Data is now suggesting that we can in fact continue to produce neurons throughout adult life. Why is this important? Loss of neurons or the inability to generate replacement cells affects various functions. One of the particularly interesting parts of the brain to be affected by neuronal loss is the hippocampus.
The role of the hippocampus
The hippocampus forms part of the emotional control centre known as the limbic system. It is so named due to its shape – it resembles a seahorse. The Greek for horse is hippos and kampos meaning sea-monster.
The hippocampus deals with memory, particularly short-term memory formation. It also has a connection with the cortex, which deals with long-term memory. The hippocampus transfers information to the cortex. Both are necessary for memory formation, and this is why if there is hippocampal damage, memory loss ensues.
The hippocampus therefore plays an important role in learning, whether our puppies and dogs are learning tricks or about the world around them.
In addition, the hippocampus is involved in control of the hypothalamic – pituitary-adrenal (HPA) axis, which is a key element of the stress response. A well-functioning hippocampus is therefore vital for an appropriate and resilient stress response.
Unfortunately, there is data that links stress with reduced hippocampal volume. It seems that stress suppresses neuronal proliferation. This smaller hippocampal volume can impede memory and learning but can also result in lower resilience to stress moving forward, and so the cycle continues.
Neurons are vital in nervous system function; loss of them is associated with poor learning, memory loss, stress resilience and more. Luckily, we’re not on the downward trend they once thought we were. There is evidence we can mitigate neuronal loss and also promote the production of new ones.
Brain Derived Neurotrophic Factor (BDNF)
There is a protein – Brain Derived Neurotrophic Factor or BDNF – that can defend the hippocampus against shrinkage and support its regrowth and repair.
BDNF is a neurotrophin, which are a family of proteins that induce the survival, development, and function of neurons. BDNF also increases energy efficiency in the brain. In humans, low levels of BDNF are linked with depression, and in dogs, low levels of BDNF are associated with separation anxiety. It seems that lifestyle choices are the biggest contributors when it comes to boosting BDNF levels in the brain.
The importance of exercise
Study after study has demonstrated that voluntary exercise increases neurogenesis in the brain, particularly in the hippocampus. Regular walks are important for your dog’s well-being, cardiovascular and skeletal health, but they are also a great way to support their brain health. Interestingly, extreme exercise has been associated with impaired cognitive function due to the overload in reactive oxygen species causing oxidative stress, so balance is key! For that reason, rest is also essential to hippocampal health! There is a diurnal rhythm of neurogenesis and as we know, dogs too are diurnal creatures. It is mainly at night that the hippocampus experiences growth due to the proteins that control the body clock. So, prioritise that night-time routine and get your full 40 winks with your dog.
Fulfilling environment
Novel enrichment activities have been noted to increase BDNF levels in the brain. What do we mean by novel enrichment activities? Essentially new challenges. It could be puzzle games, learning new tricks, navigating a new trail or hunting a new treasure (food or toy). The key element here is novelty, whilst there are generalised benefits of prior exposure to a task, there are more significant improvements when it is a new experience. Boredom is regularly linked with low BDNF levels. So, if you’ve ever fancied doing a new hobby with your dog, maybe now is the time to investigate it.
Diet
Diet can also influence BDNF levels. Omega-3 Fatty Acids have been seen to normalise BDNF levels in the brain, they are also thought to be neuroprotective in that they protect neurons from death. Great sources of Omega-3 for the dog include fatty fish like sprats, sardines, anchovies and mackerel. When including both omega-3 and vitamin B12 in the diet, higher levels of BDNF are found in the hippocampus and cortex. Vitamin B12 is a water-soluble vitamin that keeps nerve and blood cells healthy. It is also involved in energy production and more. There are no plant-sources of B12, it is produced in the gut of vegetarian animals, then absorbed into their blood stream, and makes its way around their body. Their tissue then provides B12 to whoever eats it. For that reason, sources of B12 include meat, fish, and eggs!
The importance of a heathy gut
Neurogenesis depends on a healthy gut. Healthy gut bacteria contained within the microbiome can communicate with the hippocampus via the vagus nerve which links the brain and gut. We know this because in vagotomised animals (where the vagus nerve has been severed), hippocampal neurogenesis stops.
So, maintaining a diverse microbiome is key. We can support the health of the microbiome by offering a diverse diet that meets your dog’s nutritional needs. But we also need to avoid those things that can disrupt the microbial community including overuse of antibiotics, overuse of flea/worm treatments, toxic home cleaning products and pesticide/herbicide laden food.
Things to avoid
Here are several things to avoid if you to improve neurogenesis.
Stress. Stress literally makes the brain smaller. So from puppyhood onwards try and avoid anything that may cause your dog stress.
Inflammation. a standard immune response, inflammation is a totally normal bodily process. The issue is when it becomes chronic. Reduce exposure to environmental triggers of inflammation (sensitivities) where possible, the same goes for any foods that are causing an issue. Obesity also predisposes to a pro-inflammatory state – so keep your dog lean.
Air Pollution. Whilst exercise is thought to increase BDNF levels four-fold, when this exercise is carried out in a heavily polluted area, it can actually shrink the brain! Air pollution is often implicated in neurodegeneration. Try to walk in green spaces where possible – or avoid rush hour walking in the city. Air purifiers are always a great option for the home too!
Whilst your aging dog may not be keen on the idea of learning a new trick, they probably have the cognitive capacity to do so. It’s true that if you don’t use it, you lose it. As long as we’re using our brains, and our dogs are using theirs, we have this process where new neurons can be grown. Of course, certain lifestyle factors can result in neuronal death and the inhibition of new growth, but there are ways to promote neurogenesis. We should be considering the environment we offer and whether we include any BDNF boosters like exercise, a decent diet, fulfilling activities and rest!
Article by Lisa Hannaby
References
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5808288/
https://pubmed.ncbi.nlm.nih.gov/27569259/
https://pubmed.ncbi.nlm.nih.gov/12360586/
https://www.sciencedirect.com/science/article/abs/pii/S1558787819300735
