Widespread short-latency stretch reflexes and their modulation during stumbling over obstacles.

The present study investigated whether short-latency stretch reflexes are present during human stumbling reactions. While subjects walked on a treadmill, the forward sway of the foot was unexpectedly obstructed with an obstacle. All subjects showed reflex responses with average latencies of 34-42 ms in both the upper and the lower leg flexors and extensors of the obstructed leg.

Gait adaptations during walking under visual and cognitive constraints: a study of patients recovering from limb-saving surgery of the lower limb.

The objective of this case series study was reautomatization of gait after limb-saving surgery for tumors at a laboratory of gait analysis. Twelve patients (9 males and 3 females; mean age, 38 years) who underwent limb-saving surgery of the lower limb at least 1 year previously and ten normal subjects (3 males and 7 females; mean age, 37.5 years) were studied.

Cortical facilitation of cutaneous reflexes in leg muscles during human gait.

During human gait, cortical convergence on sural nerve reflex pathways was investigated by means of transcranial magnetic stimulation (TMS) of the cortex in five phases of the step cycle during human walking on a treadmill. Muscular responses to paired electrical and magnetic stimulation were compared with the linear summation of the individual stimuli. For both the tibialis anterior (TA) and biceps femoris (BF) muscles, the averaged data of four subjects showed a significant facilitation mainly in the swing phase of the step cycle.

From cat to man: basic aspects of locomotion relevant to motor rehabilitation of SCI.

On the assumption that locomotion is partly produced by a central pattern generator (CPG) in the spinal cord of both cat and man, it is essential to learn more about how such a CPG is controlled by sensory input produced during gait. For the cat there is evidence that load receptor input both from extensor muscles and from cutaneous receptors from the foot, is able to reinforce the ongoing extensor activity in the stance phase and delay the ensuing swing phase. Original data on electrical stimulation of nerves in walking premammillary cats with one hindlimb fixed, support the notion that this type of load afferent input acts directly on the CPG.

Responses in ventral intraparietal area of awake macaque monkey to optic flow patterns corresponding to rotation of planes in depth can be explained by translation and expansion effects.

There is evidence that neurons in medial superior temporal area (MST) respond to rotation in depth of textured planes. MST neurons project to the ventral intraparietal area (VIP) and the question arises whether VIP neurons are responsive to rotation in depth as well. In the present study on awake monkeys, we have simulated movement of a flat board, covered with dots, by a computer.

Dynamic control of location-specific information in tactile cutaneous reflexes from the foot during human walking.

The purpose of the present study was to determine whether tactile cutaneous reflexes from the skin of the foot contain location-specific information during human walking. Muscular responses to non-nociceptive electrical stimulation of the sural, posterior tibial, and superficial peroneal nerves, each supplying a different skin area of the foot, were studied in both legs during walking on a treadmill. For all three nerves the major responses in all muscles were observed at a similar latency of approximately 80-85 msec.

Neurons in the ventral intraparietal area of awake macaque monkey closely resemble neurons in the dorsal part of the medial superior temporal area in their responses to optic flow patterns.

1. Neurons in the ventral intraparietal area (VIP) are known to respond to translating random dot patterns. Such responses can be explained on the basis of the input of the middle temporal area (MT) to this area.

Cortical off response tuning for stimulus duration.

To answer the question whether OFF response amplitude (firing rate) of visual cortical cells varies as a function of stimulus duration, a series of such cells from areas 17 and 18 of the cat were investigated with a stationary light bar, presented for different durations (10-3200 msec) over the receptive field. Out of a sample of 174 cells tested, 58 cells were found for which the OFF responses varied as a function of ON stimulus duration. Of these cells, 29 showed a continuous increase up to the longest duration tested, six showed a sharp tuning for medium range durations (between 50 and 400 msec) and the remaining 23 cells had an intermediate profile (increase to optimum followed by slight decrease).

Biceps femoris tendon jerk reflexes are enhanced at the end of the swing phase in humans.

The phase-dependent modulation of the biceps femoris (BF) tendon jerk reflexes was investigated in a reduced form of walking. All subjects (12) investigated showed tendon reflexes throughout the whole step cycle but the amplitude was largest in the middle and late swing phase of the ipsilateral leg. It is concluded that the normally occurring BF burst at end swing could be due to stretch-induced activity.

Quantitative gait analysis in patients with vascular parkinsonism.

Until now the clinical criteria for the diagnosis of vascular parkinsonism (VP) have been disputed. The purpose of the present study is to investigate whether quantitative gait analysis can differentiate between the gait pattern of patients with VP and the gait pattern of patients with idiopathic Parkinson's disease (PD). Twelve patients with VP, 12 patients with PD, and 10 neurologically nondiseased controls were examined by quantitative gait analysis.

Medial gastrocnemius is more activated than lateral gastrocnemius in sural nerve induced reflexes during human gait.

In humans the sural nerve was stimulated at one of 16 phases of the step cycle. In MG (medial gastrocnemius) the amplitude of the P2 responses (latency 80-93 ms) was on average 1.3 times larger than the corresponding background activity while this was 0.

Mechanically induced stumbling during human treadmill walking.

A new method to study the reactions to unexpected mechanical perturbations during human walking on a treadmill is presented. Perturbations consisted of an obstruction of the forward swinging foot during the early swing phase. These were caused by obstacles which were dropped on the treadmill in front of the subject.

Backward and forward walking use different patterns of phase-dependent modulation of cutaneous reflexes in humans.

1. The phase-dependent modulation of medium-latency (P2) (70-80 ms) responses in semitendinosus (ST), biceps femoris (BF), rectus femoris (RF), and tibialis anterior (TA) was studied with the use of low-intensity stimulation (2 times perception threshold) of the sural nerve. The shocks were given in a random order at 16 phases of the step cycle in 10 normal subjects during forward walking (FW) or backward walking (BW) on a treadmill.

Gating of sensation and evoked potentials following foot stimulation during human gait.

To investigate how gait influences the perceived intensity of cutaneous input from the skin of the foot, the tibial or sural nerves were stimulated at the ankle during walking or running on a treadmill. As compared to standing, the detection threshold for these stimuli was raised by more than 30% during the locomotion tasks. During walking, there was a phase-dependent modulation in perceived intensity of suprathreshold stimuli (1.

Human neuronal interlimb coordination during split-belt locomotion.

Human interlimb coordination and the adaptations in leg muscle activity were studied during walking on a treadmill with split belts. Four different belt speeds (0.5, 1.

Increased amplitude of cutaneous reflexes during human running as compared to standing.

The amplitude of H-reflexes is decreased during walking as compared to standing and a further reduction is seen during running as compared to walking. Does a similar reduction occur for reflexes elicited by cutaneous stimulation? To answer this question, the electromyographic (EMG) responses in biceps femoris (BF) and tibialis anterior (TA) to a 20 ms train of 5 electrical pulses, were recorded. This stimulus was applied to the sural nerve at the ankle, either at 16 different phases of the step cycle in human volunteers running on a treadmill at 8 km/h or at different isometric contraction levels of TA and BF in the same subjects during standing, imitating the postures of different phases of the step cycle.

Thalamic multiple-unit activity underlying spike-wave discharges in anesthetized rats.

In epilept WAG/Rij rats, multiple unit activity coinciding with the occurrence of spike-wave discharges was recorded under neurolept anesthesia. Recordings were made in the frontal cortex and in various nuclei of the thalamus, in specific nuclei such as the ventroposterolateral, the ventroposteromedial and the ventrolateral nuclei, as well as in non-specific nuclei such as the mediodorsal nucleus, the reticular thalamic nucleus, the interanteromedial nucleus and the intralaminar nuclei (the central medial nucleus, the centrolateral nucleus and the paracentral nucleus). Rhythmic unit firing concurrent with the spike component of the cortical spike-wave discharge was observed in deep layers of the cortex and in the following thalamic nuclei: in specific nuclei, the mediodorsal and the reticular thalamic nucleus.

Saccadic eye movements in Parkinson's disease: II. Remembered saccades--towards a unified hypothesis?

Ten patients with mild to moderate Parkinson's disease were compared with ten age-matched normal controls in a series of saccadic paradigms in order to test various hypotheses relating to the origin of the Parkinsonian saccadic defect. The paradigms comprised a reflex saccade paradigm, a standard remembered saccade paradigm, a remembered saccade paradigm with delayed centre-offset, and a remembered saccade paradigm with a second target flash immediately prior to saccade execution. Finally, subjects executed both reflex and remembered saccades in a standard remembered paradigm (the "two-saccade" paradigm).

Phase-dependent reversal of reflexly induced movements during human gait.

To investigate whether phase-dependent reversals in reflex responses on electromyography (EMG) are accompanied by movement reversals, a series of human volunteers were studied for their behavioural responses to sural nerve stimulation during running or walking on a treadmill. Low-intensity stimulation (less than 2.5 x perception threshold, T) of the sural nerve yielded facilitatory responses in the tibialis anterior muscle (TA), correlated with an induced ankle dorsiflexion (mean maximum 4 degrees) in early swing.

Facilitation of spike-wave activity by the hypnotic etomidate in a rat model for absence epilepsy.

The epileptogenic effect of the short-acting hypnotic agent etomidate was investigated in WAG/Rij rats. Animals of this inbred strain show spontaneous spike-wave discharges and are regarded as a model for absence epilepsy. A dose-dependent increase in the total amount of spike-wave activity was found, when etomidate was injected intraperitoneally in doses of 1, 2.

Temporal integration in cat visual cortex: a test of Bloch's law.

Some units in the cat visual cortex fail to respond to a briefly flashed bar and it has been suggested that such neurons function as visual integrators with a long time constant. To test this integrator hypothesis, a study was made using presentations of a bar, flashed over the receptive field for various durations and at different luminances. Some cortical cells indeed showed an increase in the time to peak latency and in the response amplitude when stimulus duration was prolonged up to 320 msec.

Selective activation of human soleus or gastrocnemius in reflex responses during walking and running.

Phase-dependent reflex modulation was studied by recording the electromyographic (EMG) responses in soleus (SOL) and gastrocnemius medialis (GM) to a 20 ms train of 5 electrical pulses, applied to the sural or tibial nerve at the ankle, in 14 volunteers walking or running on a treadmill. Although both the spontaneous activity and the reflex responses were usually similar for both muscles, instances were identified in which separate control was evident. During walking (4 km/h), activity in SOL started earlier in the stance phase than GM activity.

Gating and reversal of reflexes in ankle muscles during human walking.

Phase-dependent reflex modulation was studied by recording the electromyographic (EMG) responses in ankle flexors (Tibialis Anterior, TA) and extensors (Gastrocnemius Medialis, GM and Soleus, SOL) to a 20 ms train of electrical pulses, applied to the tibial or sural nerve at the ankle, in human volunteers walking on a treadmill at 4 km/h. For low intensity stimuli (i.e.

Suppression of the hindlimb flexor reflex by stimulation of the medial hypothalamus and thalamus in the rat.

Pentobarbital-anesthetized rats received electrical hindpaw stimulation every 10 s to elicit a maximal hindlimb withdrawal reflex. The integrated EMG response in the ipsilateral tibialis anterior was sampled by a computer which also controlled the timing of electrical stimuli applied to the brain. A suppression of the evoked flexor activity was obtained with currents below 0.