The effects of prepulse inhibition timing on the startle reflex and reaction time.

A loud acoustic stimulus has been shown to provoke a reflexive startle response and accelerate simple reaction times. However, an auditory prepulse presented in advance of a startling stimulus can reduce the effect of the startling stimulus. The current study examined the effect of the timing of the prepulse on startle-induced reaction times and the startle reflex.

Hyperoxia attenuates muscle sympathetic nerve activity following isocapnic hypoxia in humans.

Hypoxia may sensitize the carotid chemoreceptors, resulting in a sustained elevation of muscle sympathetic nerve activity (MSNA) that outlasts the hypoxic stimulus. To test this hypothesis, we determined the effect of carotid body inhibition on the sustained elevation of MSNA following isocapnic hypoxia in humans. Seven healthy subjects (5 male, 2 female) breathed 100% O(2) (hyperoxia) for 1 min before (2 interventions) and after (2-3 interventions) 20 min of isocapnic hypoxia (80% arterial oxyhemoglobin saturation).

Long-term intermittent hypoxia increases sympathetic activity and chemosensitivity during acute hypoxia in humans.

We determined the effects of 10 daily exposures of intermittent hypoxia (IH; 1 h day(-1); oxyhaemoglobin saturation = 80%) on muscle sympathetic nerve activity (MSNA, peroneal nerve) and the hypoxic ventilatory response (HVR) before, during and after an acute 20 min isocapnic hypoxic exposure. We also assessed the potential parallel modulation of the ventilatory and sympathetic systems following IH. Healthy young men (n = 11; 25 +/- 1 years) served as subjects and pre- and post-IH measures of MSNA were obtained on six subjects.

Assessing vestibular contributions during changes in gait trajectory.

Displacing prisms and galvanic stimulation were used to examine visual-vestibular interactions during target-directed gait. Participants walked towards a wall 6 m away. After taking four steps, a target on the wall, located directly in front or to the right of the participant, was illuminated.

Identifying visual-vestibular contributions during target-directed locomotion.

The purpose of this experiment was to examine the potential interaction between visual and vestibular inputs as participants walked towards 1 of 3 targets located on a barrier 5m away. Visual and vestibular inputs were perturbed with displacing prisms and galvanic vestibular stimulation (GVS), respectively. For each target there were three vision conditions (no prisms, prisms left, and prisms right), and three GVS conditions (no GVS, anode left, and anode right).

Vestibulospinal influences on lower limb motoneurons.

Galvanic vestibular stimulation (GVS) is a research tool used to activate the vestibular system in human subjects. When a low-intensity stimulus (1-4 mA) is delivered percutaneously to the vestibular nerve, a transient electromyographic response is observed a short time later in lower limb muscles. Typically, galvanically evoked responses are present when the test muscle is actively engaged in controlling standing balance.

Galvanic vestibular stimulation alters the onset of motor unit discharge.

We have previously shown that galvanic vestibular stimulation (GVS) can modulate the amplitude of the passive soleus H-reflex. This study examined whether the response resulted from a general change in excitability of the motoneuron pool or a specific modulation of individual motor units (MUs). Subjects performed slow isometric plantarflexor actions in a prone lying and kneeling position until the discharge of a single gastrocnemius MU was detected.

Relative contributions of visual and vestibular information on the trajectory of human gait.

Seven healthy individuals were recruited to examine the interaction between visual and vestibular information on locomotor trajectory during walking. Subjects wore goggles that either contained a clear lens or a prism that displaced the visual scene either 20 degrees to the left or right. A 5-s bipolar, binaural galvanic stimulus (GVS) was also applied at three times the subject's individual threshold (ranged between 1.

Interaction effects of galvanic vestibular stimulation and head position on the soleus H reflex in humans.

Objectives: The objective of this study is to measure the influence of galvanic vestibular stimulation and head-on-body alignment on the soleus H-reflex in prone human subjects.

Methods: We studied changes in the amplitude of the right soleus H-reflex to monopolar monaural galvanic stimulation in 10 healthy prone lying subjects. Trials were randomly administered according to head position (left or right) and stimulus polarity (anode or cathode).

The role of cutaneous receptors in the foot.

Cutaneous receptors in the foot sole appear to contribute to the control of human stance and locomotion. Two approaches were undertaken to establish the characteristics of the receptors in the sole. Psychophysical vibrotactile thresholds (range 25-400 Hz) were determined across the unloaded sole in young and elderly subjects.

Distribution and behaviour of glabrous cutaneous receptors in the human foot sole.

To document the activity of cutaneous mechanoreceptors in the glabrous skin of the foot sole, tungsten microelectrodes were inserted through the popliteal fossa and into the tibial nerve of thirteen healthy human subjects. A total of 104 cutaneous mechanoreceptors were identified in the glabrous skin of the foot. This sample consisted of 15 slow adapting type I (14 %), 16 slow adapting type II (15 %), 59 fast adapting type I (57 %), and 14 fast adapting type II units (14 %).