General Description

An important function of the central nervous system is to keep track of where we are, in relation to where we are going, as we move through our environment. This ability is essential for perceptual stability as well as accurate motor control. The objective of Dr. Cullen’s research program is to understand the mechanisms by which self motion (vestibular) information is integrated with signals from other modalities to accurately control eye, head, and body movements in relation to a stable external reference system. The research program studies the sensorimotor transformations required for the control of movement, by tracing the coding of vestibular stimuli from peripheral afferents, to behaviorally-contingent responses in central pathways, to the readout of accurate behavior. The experimental approach is multidisciplinary and includes a combination of behavioral, neurophysiological and computational approaches in alert behaving non-human primates and mice. Funding for the laboratory is provided by the Canadian Institutes for Health Research (CIHR), The National Institutes of Health (NIH), Canadian Space Agency (CSA), the National Sciences and Engineering Research Council of Canada (NSERC), and McGill University.

 

 

Current Research Projects

The Neuronal Encoding of Self-Motion

Recent studies in our laboratory have established that the brain distinguishes between vestibular inputs that are a consequence of our own actions and those that result from changes in the external world at the level of single neurons (reviewed in Cullen 2004). In particular, we have shown that the neurons that mediate the first stage of central processing in this system are dramatically less responsive to actively generated head movements than passively applied head movements. A major focus of the current work in our laboratory is to understand the underlying mechanisms that mediate this discrimination of self-generated movement at the circuit/systems levels. Our experiments study how adaptive strategies are manifested at the level of single neurons when the relationship between intended and actual movement is altered – since how we generate and adapt our perception of the outside world is an important question that is relevant to sensory, behavioral, and cognitive neurosciences. The findings of our experiments explain how our brain determines whether it is we or the world that is moving to guide accurate motor responses. This work has been funded by the CIHR, CSA, and McGill University.

 

The Physiology underlying Vestibular Compensation in Health and Disease

The long term goal of our NIH funded research program is to understand the physiological mechanisms that underlie vestibular compensation following peripheral vestibular damage. In normal subjects, the vestibulo-ocular reflex (VOR) effectively stabilizes gaze by moving the eye in the opposite direction to the applied head motion. Disruption of vestibular signals from one labyrinth results in asymmetries in the angular VOR, which recovers through processes of vestibular compensation. This compensation process is most effective for head movements that are of lower frequency, acceleration, and velocity. The goal of our current NIH funded research program (i.e. the experiments that are on-going in our laboratory at McGill University) is to understand the modifications that occur in VOR pathways following lesions to the labyrinth. In particular we are studying compensation at the level of the vestibular afferents and central neurons during voluntary movement and the dynamics of neuronal processing over the full range of head movement stimuli that are produced during natural behaviors. This knowledge will provide insights into the treatment of vestibular disorders; patients who suffer from vertigo, dizziness and disorientation are extremely common in the clinics, however most often the fundamental causes of these symptoms cannot be determined.

 

The Neural Control of Disjunctive Eye Movements

The current goal of our NSERC funded research program is to understand how the brain moves the two eyes by different amounts and/or directions. For example, eye movements of different angles are required whenever we voluntarily shifts our point of visual attention from a near to a far target (and vice versa). We have already made substantial progress in establishing that the premotor circuits that control saccadic and vergence eye movements are not independent. We are currently identifying the source of the upstream drive that shapes the monocular signals encoded by premotor saccadic neurons during disjunctive eye movements.