Vestibular Dysfunction after Subconcussive Head Impact

Abstract

Current thinking views mild head impact (i.e., subconcussion) as an underrecognized phenomenon that has the ability to cause significant current and future detrimental neurological effects. Repeated mild impacts to the head, however, often display no observable behavioral deficits based on standard clinical tests, which may lack sensitivity. The current study investigates the effects of subconcussive impacts from soccer heading with innovative measures of vestibular function and walking stability in a pre- 0-2 h, post- 24 h post-heading repeated measures design. The heading group (n = 10) executed 10 headers with soccer balls projected at a velocity of 25 mph (11.2 m/sec) over 10 min. Subjects were evaluated 24 h before, immediately after, and 24 h after soccer heading with: the modified Balance Error Scoring System (mBESS); a walking stability task with visual feedback of trunk movement; and galvanic vestibular stimulation (GVS) while standing with eyes closed on foam. A control group (n = 10) followed the same protocol with no heading. The results showed significant decrease in trunk angle, leg angle gain, and center of mass gain relative to GVS for the heading group compared with controls. Medial-lateral trunk orientation displacement and velocity during treadmill walking increased immediately after mild head impact for the heading group compared with controls. Controls showed an improvement in mBESS scores over time, indicating a learning effect, which was not observed with the heading group. These results suggest that mild head impact leads to a transient dysfunction in vestibular processing, which deters walking stability during task performance.

Keywords: behavioral assessments; head trauma; human studies; outcome measures; sensory function.

FIG. 1.

Experimental setup for standing and walking posture control assessment. (A) Standing on foam with eyes-closed during galvanic vestibular stimulation. (B) Schematic of a subject walking the treadmill with visual feedback system.

FIG. 2.

(A) Modified Balance Error Scoring System (mBESS) error scores and (B) performance scores on walking task across sessions for the experimental group (EXP) and control group (CON). Error bars represent standard error of the mean. *Represents significant group effect from analysis of covariance with pre-test set as covariate (p < 0.05). **Represents significant time effect within group from two-tailed paired t test (p < 0.017).

FIG. 3.

Gain response and root mean square (RMS) from galvanic vestibular stimulation (GVS) in anterior/posterior (AP) direction. Experimental (EXP) group shows significant decrease in gain from Pre to Hr0 and significant increase in gain from Hr0 to Hr24 for leg angle, trunk angle, and center of mass (COM). RMS across all conditions shows no changes in overall sway across time and group. (A) Gain of leg segment angle relative to GVS. (B) Gain of trunk segment angle relative to GVS. (C) Gain of COM relative to GVS. (D) Overall sway of leg angle in RMS during GVS. (E) Overall sway of trunk angle in RMS during GVS. (F) Overall sway of COM in RMS during GVS in EXP and control (CON) groups. Error bars represent standard error of the mean. *Represents significant group effect from analysis of covariance with pre-test set as covariate (p < 0.05). **Represents significant time effect from two-tailed paired t test (p < 0.017).

FIG. 4.

Trunk orientation during walking posture assessment in experimental group (EXP) and control group (CON). (A) Root mean square (RMS) of displacement of trunk orientation in medial-lateral (ML) direction. (B) RMS velocity of trunk orientation in ML direction. Error bars represent standard error of the mean. *Represents significant group effect from analysis of covariance with pre-test set as covariate (p < 0.05). **Represents significant time effect from two-tailed paired t test (p < 0.017).