Characterizing Brain Activation and Postural Response During Concurrent Cognitive Tasks in the Presence of Optic Flow Stimulation: A Functional Near-Infrared Spectroscopy Study

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PROJECT SUMMARY Human postural control involves multiple sensory integrations from visual, somatosensory, and vestibular inputs. Due to a decline in somatosensation and vestibular function that occurs with aging, vision becomes the dominant sensory input used to maintain balance in elderly adults. Studies have used optic flow (OF) to examine the effect of visual input on postural control. While optic flow stimulus can be presented through traditional PC monitor setups, the advent of consumer grade virtual reality (VR) head mounted displays has provided new options. An immersive VR environment is advantageous because it can provide OF stimulus to induce a self-motion illusion that provokes postural responses while also isolating the subject from outside stimuli. In addition to visual information, attention is critical for older individuals to maintain good balance. Studies have used dual-task paradigms, such as performing a concurrent cognitive task along with a balance task, to examine the cognitive demands associated with postural control. However, the mechanisms of sensory integration processing and neural resource allocation in the human brain have not been fully investigated in real balance tasks with concurrent cognitive tasks. A novel neuroimaging method, functional near-infrared spectroscopy (fNIRS), provides us the opportunity to explore the underlying mechanism of postural control in the human brain. The purpose of this research is to investigate physiological limitations when processing OF information and observe the neural resource allocation during dual-task conditions. In this study, healthy younger adults (aged 25-45 y.o., n = 24), healthy older adults (aged 65-85 y.o., n = 24), and older adults at risk of falling based on the STEADI and clinical balance/gait assessments (aged 65-85 y.o., n = 24) will be recruited. In the first visit subjects will be asked to wear a VR head mounted display that will present the OF stimulation. Particle movement speed will vary between six levels, 0 m/s (static), 5m/s, 10 m/s, 15 m/s, 20 m/s, and 25 m/s. The nonstatic OF speeds will be contracted to the static OF (0 m/s) in a block design, (A1-B-A2), for a total of six conditions. Each block will last for 30 seconds. In the second visit, the subjects will perform two auditory reaction time tasks while receiving OF stimulation at the speeds of 5 m/s and 20 m/s. During the two study visits fNIRS will be used to measure brain activity in regions of interest (ROIs) including the bilateral prefrontal cortices, superior temporal areas, and temporoparietal junctions. We will compare the group, gender, and hemisphere differences in the ROIs. A repeated measure ANOVA will be used to analyze the reaction time and postural sway data to examine the effects of Group (younger, older, and older adults with fall risks), OF speed (six OF speeds), Block (A1, B, and A2), and their interactions.