All animal behaviour depends on the correct selection and implementation of motor commands. Motor output though must be constantly updated, adapted and maintain enough flexibility so that movement can be sustained with changes in behavioural goal, internal state or environmental context. The goal of our laboratory is to understand how animals use a combination of sensory input and past experience to generate, select and updates motor plan in dynamic environments. Below is a brief description of some of the ongoing projects in the lab.
How we perceive and respond to a sensory stimulus depends heavily on the environmental context. For example, the sensory-motor reflexes that maintain our balance are generally more prominent when our balance is threatened. How does the brain interpret one particular environment as being threatening, and how does it then use this information to adapt sensory-motor reflexes?
The lateral vestibular nucleus (LVN) can generate postural reflexes that maintain balance. Two complimentary approaches are employed in our study of how LVN circuit dynamics are altered in different environmental contexts. First, we are examining the input circuitry to the LVN in order to determine which circuits could influence reflex gain. Second, we are developing mouse behavioural approaches that allow us to tune the level of balance threat. This complementary circuit and behavioural approach should help us to understand how the brain can control the gain of sensory-motor reflexes in different environments.
Neurons in the mouse lateral vestibular nucleus labelled by fluorogold injection in the spinal cord.
Whether running for the bus, reaching for a book or stepping onto an escalator most of the movements we make present two problems for the brain:
Limb and body movements can disrupt our balance, so how does the brain ensure our balance is stable when the body is in motion?
Self-generated limb and body movements activate sensory receptors in the same way as externally applied perturbations. How does the brain distinguish between these two types of sensory input?
The nervous system solves these seemingly separate problems in the same way, by constantly predicting the consequences of its own actions and making according adjustments to sensory-motor.
Preparing for movement through anticipatory postural adjustments
Every limb and body movement has the potential to destabilise the body. The simple act of taking a step, or reaching for an object can move the body’s weight too far from the base of support leading to a fall. To prevent this, the nervous system predicts the consequence of a movement before it is performed and generates an anticipatory postural adjustment (APA) – a pre-emptive adjustment of trunk and limb muscles in anticipation of the upcoming movement. In the lab we study how APAs are generated in order to probe how the brain predicts the consequences of its own movements.
Tuning of vestibular processing during movement
Sensory input from the vestibular system provides information about acceleration and rotation of the head. However, the brain can alter this sensory inflow through the actions of the efferent vestibular system (EVS), a group of brainstem neurons that innervate the vestibular periphery and can alter firing in hair cells and vestibular afferents. One hypothesis regarding the function of the EVS is that these neurons receive a copy of motor output and use this information to tune the vestibular system accordingly. In the lab, we are using a combination of mouse genetics and viral approaches to target the EVS and understand its role in distinguishing self-generated and externally imposed motion.
Neurons in the mouse brain that directly innervate postural circuits, identified using monosynaptic rabies tracing.
Central to our goal of understanding vestibular-motor behaviour is the availability of tools for the targeting, manipulation and mapping of neural circuits. Our lab, therefore, also develops new viral technologies that allow us to map the connections between neurons as well as monitor and manipulate their activity. It is our hope that the technology developed in our lab will aid both in our goal of understanding sensory-motor circuits, as well as being valuable to the wider neuroscience community.
A rabies virion magnified approximately one million times. We develop rabies-based technologies to map connections between neurons.
From: Murray, 2018