Associate Professor Christian Stricker is head of the Stricker Group at the John Curtin School of Medical Research. His research interests include computational modelling, synaptic transmission, information transfer of learning and memory, and cell signalling in the immune system. Professor Stricker sat down with me to talk about our understanding of neural plasticity.
Neural plasticity refers to the ability of our brains to acquire long-lasting changes in its functionality in response to environmental changes. At the cellular level, connections between neurons can strengthen, and on a larger scale, the brain can restructure its connections. The result of this is more efficient communication in your brain, for whatever behaviour it is trying to facilitate.
While the exact mechanisms may still be unclear, Professor Stricker highlighted the importance of neural plasticity during our evolution, posing the question: ‘How could you otherwise survive in an environment where there is continual change without actually having adaptable networks and structures in the brain?’
Nervous systems existed in the first algae, yet the same principles of adaptability have carried over into multi-cellular life. ‘[Adaption is] one of the key drivers of the evolution of the central nervous system’. While our nervous system have allowed humans to command many different environments, Stricker believes ‘the distribution of the humans on the planet is a testament to the fact that we are highly adaptable.’
Stricker admits that as a neuroscientist who primarily focuses on animal models, it is difficult to comment on cognition. What he did say however, was that while plasticity is not necessarily linked to IQ, ‘intelligence is ultimately linked to how much knowledge we can store’, and that information storage, or learning and memory, do lie within the domain of plasticity.
In terms of the hierarchy, Stricker says that ‘it’s memory plus the response to the particular situation you are in that ultimately gives the learning’. He went on to say that ‘memory is the static aspect of it while learning is the more dynamic aspect to it which ultimately results in a noticeable change in your behaviour.’ In short, you cannot learn without memory, which we know is an aspect of plasticity. Yet, Stricker hinted that there might be some molecular link to intelligence that could have a role in a specific type of plasticity.
Regenerative plasticity allows stroke victims who’ve lost brain tissue to rehabilitate. ‘[Stroke patients] can retune the networks so that other areas in the brain which would have been dormant or not so active can now take over so that you can again function in your normal way.’ Stricker described the mechanism through which quadriplegics can control technology through eye movements as testament to the degree to which adult brains are still plastic. He also explained that the rehabilitation of stroke patients might be so successful because, unlike normal plasticity, during regenerative plasticity decaying tissues serve as a beacon for new nerve fibre reconstruction.
In terms of Alzheimer’s, the issue is more complex, since mechanisms of plasticity decline at an older age. Utilizing new sensory inputs as a treatment, however, can still be beneficial as ‘to some extent there can be some reactivation, or at least the slope of decay can be halted’.
Paradigms in Science
Throughout his career, Stricker has been influential in challenging standard dogmas in neuroscience, including mechanisms relevant to adult plasticity and long term memory. While researchers these days tend to be more relaxed, Stricker acknowledges the benefit of researchers who take extreme stances: It’s quite often very fruitful to explore the radical stances of hypotheses, for example, it’s all presynaptic or postsynaptic … in hindsight at least they were driving the field in their stances.’
One major aspect of memory and plasticity that is not well understood is how memories are recalled from their physical storage in the brain.
Stricker describes cutting edge experiments done by Tonegawa at MIT where memories in mice can be artificially recalled by shining a light on light sensitive parts of the storage. ‘For that we need to trigger it ourselves, we do not know what the trigger is or how the brain comes about the trigger under normal conditions … how it is actually being read out is far from clear,’ Stricker said. He went on to say that learning how we access memories once they have been laid down could potentially challenge existing conceptions in the field.
Understanding how this activation occurs could have potential implications for treating PTSD.
Professor Stricker explained that if we knew how memories are recalled, we would know how to erase them, which would be especially poignant for PTSD or otherwise traumatised patients. ‘Because of that attachment of an emotional dimension to [a memory],’ Stricker said, ‘it can actually be that you can never really truly forget it’.
This link between emotion and memory formation is an area of research that Prof Stricker himself is exploring. He believes the answer may lay in neuromodulators like serotonin or dopamine. ‘There is still an emotional tag that goes with [memory formation], and that is typically given by neuromodulators’, he said. Stricker hopes that by studying these systems, we will be able to give survivors of traumatic events the gift of forgetting. ‘There are amazing changes in the short term dynamic plasticity, so these neuromodulators, they actually really do stuff in the network, they really change it.’