EyeProprio

The paper “Role of somatosensory cortex in visuospatial attention” by Balslev, Odoj and Karnath has just been accepted for publication at J Neuroscience.

Abstract

The human somatosensory
cortex (S1) is not among the brain areas usually associated with visuospatial
attention. However, such a function can be presumed, given the recently
identified eye proprioceptive input to S1 and the established links between
gaze and attention. Here we investigated a rare patient with a focal lesion of the
right postcentral gyrus that interferes with the processing of eye proprioception
without affecting the ability to locate visual objects relative to her body or to
execute eye movements. As a behavioural measure of spatial attention we recorded
fixation time during visual search and reaction time for visual discrimination
in lateral displays. In contrast to a group of age-matched controls, the patient
showed a gradient in looking time and in visual sensitivity towards the
midline. Because an attention bias in opposite direction, towards the
ipsilesional space, occurs in patients with spatial neglect, in a second study
we asked whether the incidental co-injury of S1 together with the
neglect-typical perisylvian lesion leads to a milder neglect. A voxelwise
lesion behaviour mapping (VLBM) analysis of a group of right hemisphere stroke
patients supported this hypothesis. The effect of an isolated S1 lesion on visual
exploration and visual sensitivity as well as the modulatory role of S1 in
spatial neglect, suggest a role of this area in visuospatial attention. We hypothesize
that the proprioceptive gaze signal in S1, whereas playing only a minor role in
locating visual objects relative to the body, affects the allocation of
attention in the visual space.

Funded by the Danish Medical Research Councils (DB). With thanks to RW for helping us conducting this study.

On September 1 I will be moving to the School of Psychology and Neuroscience at the University of St Andrews. Goodbye Germany, hello Scotland !

My first paper co-authored with my PhD student. I feel so grown up.

Odoj and Balslev. 2013. Visual sensitivity shifts with perceived eye position. J Cogn Neurosci 25: 1180

We show that inhibitory rTMS over the somatosensory cortex in healthy humans changes the allocation of attention in the visual space. We found that a decrease of excitability of this brain region causes changes in visual sensitivity to favor stimuli that appear at locations nearer the subject’s
midline, regardless of their location in retinotopic coordinates. The
midline-to-periphery gradient in the body-centred space mirrors the organization
of the eye proprioceptive area, where neural firing increases with gaze
eccentricity for all gaze directions, and differs from the left-right gradient
in the eye-centred space that
characterizes the organization of the FEF and SC.

Using a sclera lens we induced a sustained rotation
of the non-viewing, dominant eye, stimulating the extraocular muscle
proprioceptors. While participants viewed a display with the non-dominant eye,
this procedure improved visual detection in the hemifield located in the
direction of this rotation.

( Balslev, Newman and Knox. Extraocular muscle afferent
signals modulate visual attention. Investigative Ophthalmology & Visual Science, in press)

This paper has the proofs already online

Daniela Balslev, Hartwig R. Siebner, Olaf B. Paulson, Tanja Kassuba. (2012) The cortical eye proprioceptive signal modulates
neural activity in higher-order visual cortex as predicted by the variation in
visual sensitivity. Neuroimage (in press) http://www.ncbi.nlm.nih.gov/pubmed/22521251

… and this paper just got accepted, I uploaded my final version on the website:

Daniela Balslev, Marc Himmelbach, Hans-Otto Karnath, Svenja Borchers, Bartholomaeus Odoj (2012) Eye proprioception used for visual localization only
if in conflict with the oculomotor plan. J Neuroscience (in press)

http://www.danielabalslev.dk/proofs.pdf

Eye muscle proprioceptive manipulation confirms spatial bias in visual attention towards the perceived direction of gaze

Daniela Balslev, William Newman, Paul C. Knox

My talk is scheduled on Thursday sept 1 at 15:30.

Our conclusion is that attention is involuntarily captured in the perceived direction of gaze. By using passive eye movement, this study provides more direct evidence of the role of eye proprioception in the allocation of attention, than my previous study where we interfered with the cortical processing of eye proprioception using repetitive transcranial magnetic stimulation (rTMS) over the somatosensory cortex.

The experiment was carried out at the University of Liverpool in collaboration with Drs. Knox and Newman. We used a scleral lens to manipulate the eye muscles and measured the consequences of this proprioceptive stimulus on visual accuracy. This proceedure was invented by Gabriel Gauthier and is considered “the golden standard” for testing the effects of eye proprioception on behavior in humans. I was very lucky to work with Paul Knox who is one of the few experts worldwide in using this method, and with William Newman, an ophthalmology consultant who kindly offered a chunk of his very busy time to make sure that the eyes of the experiment participants stayed safe.

The scleral lens is very similar with a hard contact lens that is used in patients. The lens is modified by attaching a tube – through which light suction is created to fix the lens to the cornea – and a stalk – which is fixed in a static holder. First the participant fixates laterally at 10 degrees, allowing us to block the dominant eye in this position. Then s/he is instructed to fixate centrally, causing the non-dominant, viewing eye to rotate back, whereas the non-viewing eye remains deviated. Although this eye returns centrally, its position is perceived to be slightly (~2 degrees) rotated in the direction of the dominant eye. This dissociates the real direction of gaze from the perceived direction of gaze and allows us to test visual detection for targets that are retinotopically equidistant, but presented at different distances from the perceived direction of gaze.

The procedure is not painful, only unpleasant – like putting contact lenses in and out of the eyes…

The abstract of my talk is here.

See you in Toulouse maybe…

Daniela will give a Young investigator talk at the Gordon Research Conference on Eye Movements on Monday 01 august 2011 at the University of New England http://www.grc.org/programs.aspx?year=2011&program=eyemove

Eye proprioception used for visual localization only if in conflict with
the oculomotor plan

Daniela Balslev1,2, Marc Himmelbach1, Hans-Otto Karnath1, Svenja Borchers1, Bartholomaeus Odoj1

1 Center of Neurology and Hertie Institute for Clinical Brain Research, University of Tuebingen , Germany; 2Department of Psychology, University of Copenhagen, Denmark

There are two hypotheses about how the efference copy of the motor command and the extraocular muscle proprioception are combined to locate retinal objects relative to the body: 1. only the efference copy is used whereas proprioception is a slow recalibrator of the forward model [Steinbach, 1987, Acta Psychologica, 63, 297-306] and 2. both signals are used together as a weighted average [Gauthier et al, 1990, Science, 249(4964), 58-61]. We tested these hypotheses in a patient (RW) with a circumscribed lesion of the right postcentral gyrus, that overlaps the eye proprioceptive representation [Balslev et al., 2011, Human Brain Mapping, 32, 624-631]. RW was as accurate and precise as the control group (n=19) in locating a lit LED that she viewed through the eye contralateral to the lesion (p > 0.6). However, when the task was preceded by a brief (<1s) and gentle push to the closed eye, which perturbs eye position and stimulates eye proprioceptors in the absence of a motor command, RW’s accuracy decreased (p<0.001). We suggest that eye proprioception is used only as a back-up during visual localization. Proprioception is compared with the efference copy and incorporated into the eye position estimate in conditions with a mismatch.

Acknowledgments: Funded by the Danish Medical Research Councils and a Marie Curie intra-european fellowship (DB). Grant numbers: 09-072209 and PIEF-GA-2009-252424.