Assessment of Neurological Impairment and Recovery Using Statistical Models of Neurologically Healthy Behavior.

While many areas of medicine have benefited from the development of objective assessment tools and biomarkers, there have been comparatively few improvements in techniques used to assess brain function and dysfunction. Brain functions such as perception, cognition, and motor control are commonly measured using criteria-based, ordinal scales which can be coarse, have floor/ceiling effects, and often lack the precision to detect change. There is growing recognition that kinematic and kinetic-based measures are needed to quantify impairments following neurological injury such as stroke, in particular for clinical research and clinical trials.

Impairments in Cognitive Control Using a Reverse Visually Guided Reaching Task Following Stroke.

Background: Cognitive and motor function must work together quickly and seamlessly to allow us to interact with a complex world, but their integration is difficult to assess directly. Interactive technology provides opportunities to assess motor actions requiring cognitive control.

Objective: To adapt a reverse reaching task to an interactive robotic platform to quantify impairments in cognitive-motor integration following stroke.

Robotic tests for position sense and movement discrimination in the upper limb reveal that they each are highly reproducible but not correlated in healthy individuals.

Background: Robotic technologies for neurological assessment provide sensitive, objective measures of behavioural impairments associated with injuries or disease such as stroke. Previous robotic tasks to assess proprioception typically involve single limbs or in some cases both limbs. The challenge with these approaches is that they often rely on intact motor function and/or working memory to remember/reproduce limb position, both of which can be impaired following stroke.

A postural unloading task to assess fast corrective responses in the upper limb following stroke.

Background: Robotic technologies to measure human behavior are emerging as a new approach to assess brain function. Recently, we developed a robot-based postural Load Task to assess corrective responses to mechanical disturbances to the arm and found impairments in many participants with stroke compared to a healthy cohort (Bourke et al, J NeuroEngineering Rehabil 12: 7, 2015). However, a striking feature was the large range and skewed distribution of healthy performance.

KAPS (kinematic assessment of passive stretch): a tool to assess elbow flexor and extensor spasticity after stroke using a robotic exoskeleton.

Background: Spasticity is a common sequela of stroke. Traditional assessment methods include relatively coarse scales that may not capture all characteristics of elevated muscle tone. Thus, the aim of this study was to develop a tool to quantitatively assess post-stroke spasticity in the upper extremity.

Rapid and flexible whole body postural responses are evoked from perturbations to the upper limb during goal-directed reaching.

An important aspect of motor control is the ability to perform tasks with the upper limbs while maintaining whole body balance. However, little is known about the coordination of upper limb voluntary and whole body postural control after mechanical disturbances that require both upper limb motor corrections to attain a behavioral goal and lower limb motor responses to maintain whole body balance. The present study identified the temporal organization of muscle responses and center of pressure (COP) changes following mechanical perturbations during reaching.

A robot-based behavioural task to quantify impairments in rapid motor decisions and actions after stroke.

Background: Stroke can affect our ability to perform daily activities, although it can be difficult to identify the underlying functional impairment(s). Recent theories highlight the importance of sensory feedback in selecting future motor actions. This selection process can involve multiple processes to achieve a behavioural goal, including selective attention, feature/object recognition, and movement inhibition.

Feedback control during voluntary motor actions.

Humans possess an impressive ability to generate goal-oriented motor actions to move and interact with the environment. The planning and initiation of these body movements is supported by highly distributed cortical and subcortical circuits. Recent studies, inspired by advanced control theory, highlight similar sophistication when we make online corrections to counter small disturbances of the limb or altered visual feedback.

Selective weighting of cutaneous receptor feedback and associated balance impairments following short duration space flight.

The present study investigated the perception of low frequency (3 Hz) vibration on the foot sole and its relationship to standing balance following short duration space flight in nine astronauts. Both 3 Hz vibration perception threshold (VPT) and standing balance measures increased on landing day compared to pre-flight. Contrary to our hypothesis, a positive linear relationship between these measures was not observed; however astronauts with the most sensitive skin (lowest 3 Hz VPT) were found to have the largest sway on landing day.

Selective skin sensitivity changes and sensory reweighting following short-duration space flight.

Skin sensory input from the foot soles is coupled with vestibular input to facilitate body orientation in a gravitational environment. Anecdotal observations suggest that foot sole skin becomes hypersensitive following space flight. The veritable level of skin sensitivity and its impact on postural disequilibrium observed post space flight have not been documented.

Single low-threshold afferents innervating the skin of the human foot modulate ongoing muscle activity in the upper limbs.

We have shown for the first time that single cutaneous afferents in the foot dorsum have significant reflex coupling to motoneurons supplying muscles in the upper limb, particularly posterior deltoid and triceps brachii. These observations strengthen what we know from whole nerve stimulation, that skin on the foot and ankle can contribute to the modulation of interlimb muscles in distant innervation territories. The current work provides evidence of the mechanism behind the reflex, where one single skin afferent can evoke a reflex response, rather than a population.

Cooling reduces the cutaneous afferent firing response to vibratory stimuli in glabrous skin of the human foot sole.

Skin on the foot sole plays an important role in postural control. Cooling the skin of the foot is often used to induce anesthesia to determine the role of skin in motor and balance control. The effect of cooling on the four classes of mechanoreceptor in the skin is largely unknown, and thus the aim of the present study was to characterize the effects of cooling on individual skin receptors in the foot sole.

Skin sensory information from the dorsum of the foot and ankle is necessary for kinesthesia at the ankle joint.

Previous research has shown that skin is capable of providing kinesthetic cues at particular joints but we are unsure how these cues are used by the central nervous system. The current study attempted to identify the role of skin on the dorsum of the ankle during a joint matching task. A 30cm patch of skin was anesthetized and matching accuracy in a passive joint matching task was compared before and after skin anesthetization.

Modulation of the soleus H-reflex following galvanic vestibular stimulation and cutaneous stimulation in prone human subjects.

There is evidence to suggest that vestibular and somatosensory inputs may interact when they are processed by the central nervous system, although the nature of the individual sensory contributions to this interaction is unknown. We examined the effects of a combined vestibular and cutaneous conditioning stimulus on the motoneuron pool that supplies the soleus muscle via the Hoffman reflex (H-reflex). We applied galvanic vestibular stimulation (GVS; bipolar, binaural, 500 ms, 2.

Age-related changes in avoidance strategies when negotiating single and multiple obstacles.

The aim of this research was to describe age-related changes in locomotor adjustments during obstructed gait and expand and build from the current body of literature describing single obstacle avoidance strategies by including trials in which the subjects stepped over two identical obstacles placed in series. We observed young adults (YA: N = 8; aged 23.1 +/- 2.

Control strategies used by older adults during multiple obstacle avoidance.

The purpose of our study was to determine the methods of control over the center of mass (COM) utilized by older adults when navigating a functional obstacle course. The course included three different types of obstacles placed closely in series requiring subjects to walk around, step over and duck under. Optoelectric cameras were used to record kinematic data as older adults navigated the course under normal and low lighting and different obstacle contrast conditions.

Middle-old and old-old retirement dwelling adults respond differently to locomotor challenges in cluttered environments.

Obstacle navigation during locomotion was investigated in older adults using an obstacle course paradigm under different ambient lighting conditions. Similar strategies for obstacle navigation were observed between the two age groups studied (middle-old: 75-85 years and old-old adults: 85 years and older), however old-old individuals were "less" successful at avoiding obstacles. Differences observed between the two age groups in obstacle course performance may be attributed to changes in spatial reference frames that occur with age and/or differences in perceived threat of obstacles in the travel path.