Marsden 2009-II: So much to learn from synapses
Johanna Montgomery from the University of Auckland will study what happens during development to determine what synaptic connections are maintained and which are eliminated
After neurons are born in the embryo they need to make connections (synapses) with their appropriate targets. Developmental neurobiologists have known for some time that many synaptic connections that are initially made are later eliminated. Why and how this happens is at the core of understanding brain development, brain plasticity and how different brain areas come to be connected the way they are. But this is really hard to study because the process is very hard to monitor over time. Johanna and her colleagues are now able to monitor this process in the developing inner ear (cochlea) because they can identify those synapses that persist in the adult and those that don’t. In their new model, they will record simultaneously the electrical activity from the sensory hair cells and the tiny nerve terminals beneath them, and determine what is different between the two types of synapses, and whether these differences can explain why some synapses are destined to stay and others to be removed. They will also examine how normal auditory experience may affect the way that this process is regulated. This is a great project because it not only addresses a fundamental aspect of the development of neuronal connections but will also provide important information as to what happens to the wiring of the ear as a result of abnormal auditory experience which has profound implications for our understanding of deafness.
John Reynolds from the Univesity of Otago will study how synaptic connections change during learning
Our brains attach causal significance to our actions. For example, if we turn on a light at home and suddenly there is a blackout in the entire city we immediately assume we are somehow are responsible for it. Chances are we were not. But our brain reaches this conclusion based on the timing between both events, because this is how the brain learns the relationship between an action we perform and a sensory event that follows, that is , cause-consequence relationships. John proposes to study how these relationships are built in the brain, and suggest that dopamine in the striatum (that is part of the basal ganglia) is somehow involved in this process. If he is right, then changes in synaptic activity should follow cause-consequence learning. To record the activity of synapses you need to record from inside the cell, and although this is not an easy thing to do, John has mastered the technique to do so in an anaesthetised animal (I must say very few people are actually able to do this!). They chose to record from the synapses in the striatum during this type of learning because it is an area known to be involved in reward-related learning, skill acquisition, the formation of stimulus-response associations and lots of other things. It also contains the largest amount of dopamine in the brain and receives inputs from virtually all areas of the cerebral cortex. The big thing behind this project is that they will be able to correlate synaptic efficacy and the effects of altering the timing of the dopamine signal in the entire animal with a very specific behavioural task: did A cause B? I, personally, can’t wait to hear what they find!
Paul Smith from the University of Otago will look at how our balance organ may be involved in memory
I, for one, never thought of my ear being involved in memory. But it turns out that it is. The vestibular system provides the brain with information about our head movement and position, and therefore it contributes to the formation of memories about places and the environment. Damage to the balance organ (vestibular system) in the ear causes memory deficits, and it looks like the vestibular system is necessary for the retrieval of some types of memory. What Paul proposes to do is to examine whether he can enhance memory retrieval by stimulating the vestibular system. If the hypothesis is correct, this work will change our understanding of how memories are formed and retrieved, and, of course, have huge implications for therapies for memory disorders.