Age-related changes in visual-vestibular interactions in healthy subjects (an fMRI study)

Introduction and Aims: The concept of an inhibitory interaction between the visual and the vestibular systems at the cortical level as the basis for interactions between the different sensory systems is supported by several previous functional imaging studies using magnetic resonance imaging (fMRI) and positron emission tomography [1–5]. The aim of our study was to broaden this concept by addressing the question how the specific pattern of visual-vestibular interactions changes with age.

Methods: In a group of 18 healthy right-handed subjects, aged 20 to 80 years, horizontal optokinetic nystagmus (OKN) was visually elicited while fMRI and video-oculography (VOG) were performed. Additionally, tests for visual acuity, ocular-dominance, handedness and neuropsychological deficits (Montreal Cognitive Assessment test) were done in each subject. Data analysis was performed using SPM5.

Results: The group analysis revealed the well-known visual-vestibular activation/deactivation pattern. A paired t-test for hemispheric differences using flipped and unflipped images revealed stronger BOLD signal increases located in the visual cortex V1 (BA17), V2 (BA18), V3, V4, the optic radiation and the lateral occipital cortex within the right hemisphere. Further BOLD signal increase was located in the anterior insula within the left hemisphere. Significantly higher signal within the left hemisphere compared to the right hemisphere was found in the anterior thalamus and cingulum, while significantly higher signal within the right hemisphere was found in the posterior insula, posterior thalamus and corticospinal tract.

Fig.1: BOLD signal differences between hemispheres

Correlation analysis showed that the deactivation in the right inferior temporal gyrus decreased with age.

Fig.2: Negative correlation for age for deactivation in the inferior temporal gyrus

Conclusion: These data support the concept of visual-vestibular interaction. They further show an area of age-related changes in the BOLD signal located in the right inferior temporal gyrus, lateral, anterior and caudal to MT/V5. The inferior temporal gyrus is an associative visual area assumed to be involved in the representation of complex object features and especially multimodal sensory integration.

References:

[1] Dieterich M. et al. Exp Brain Res (2003)

[2] Bense S. et al. Exp Brain Res (2006)

[3] Brandt T. et al. Brain (1998)

[4] Brandt T. et al. Ann. N.Y. Acad. Sci. (2002)

[5] Stephan T. et al. Neuroimage (2005)

Acknowledgements: This study was supported by Deutsche Forschungsgemeinschaft, Grant number GRK 1091, 2 Orientation and Motion in Space.