Daniela Balslev  

Research

Eye proprioception

Without an accurate cortical representation of eye position in the orbit it would be difficult to reach to visual targets or to match an unknown person and a voice in a crowd. Eye position helps locate visual stimuli relative to head or body and thus, by aligning vision with other sensory and motor information may contribute to building abstract, multimodal maps for directing attention or for exploring the space. It was long believed that the efference copy of the oculomotor command alone provides the eye position estimate, whereas the proprioceptive receptors in the extraocular muscles had no contribution at all. Pioneering research has demonstrated that the human brain takes proprioceptive input into account when estimating eye position, however the method used to dissociate the proprioceptive output from the oculomotor command involved the application of a suction lens on the cornea to allow the manipulation of the eye. Safety concerns obviously limit the use of this method.  Recently, a neuronal signature of the proprioceptive eye position signal has been traced in the monkey somatosensory cortex. Extending these invasive recordings in monkeys, my experiments in healthy humans showed that a lasting decrease of activity in the somatosensory cortex induced with repetitive transcranial magnetic stimulation alters the perception of one's own eye position and reduces the ability to correct for a proprioceptive perturbation (Balslev and Miall, J Neurosci, 2008). Using this method I found that the proprioceptive eye position signal in the somatosory cortex modulates the distribution of attention in the visual space (Balslev, Gowen and Miall, J Cogn Neurosci, 2011).Thus, not only the oculomotor command but also the eye proprioception signal links the focus of gaze with the focus of attention.

Hand proprioception and its influence on processing visual information

Limb muscles too have receptors that sense stretch.  By integrating inflow across receptors it is possible to extract the position of the limb . It is very difficult to "silence" this inflow in a working muscle.  During my PhD, I have developed a safe and painless method for acute proprioceptive deafferentation in healthy people using repetitive transcranial magnetic stimulation over the hand-contralateral somatosensory cortex (Balslev et al., J. Neurosci 2004). I have been using this method  to show that during movements, the proprioceptive feedback facilitates the processing of  visual hand feedback (Balslev et al., J Vision 2007) . The mechanism of this effect is presumably the interaction between proprioception and vision in the allocation of attention in space. That is, during movement proprioceptive stimuli  draw attention towards the location of the hand facilitating visual perception (Jackson, Miall and Balslev,  Exp Brain Res, in press).  In conclusion, vision and proprioception are not only fused into a single, more robust percept as previously thought but also  interact in the allocation of attention in space.