The auditory startle response in post-traumatic stress disorder.

Post-traumatic stress disorder (PTSD) patients are considered to have excessive EMG responses in the orbicularis oculi (OO) muscle and excessive autonomic responses to startling stimuli. The aim of the present study was to gain more insight into the pattern of the generalized auditory startle reflex (ASR). Reflex EMG responses to auditory startling stimuli in seven muscles rather than the EMG response of the OO alone as well as the psychogalvanic reflex (PGR) were studied in PTSD patients and healthy controls. Ten subjects with chronic PTSD (>3 months) and a history of excessive startling and 11 healthy controls were included. Latency, amplitude and duration of the EMG responses and the amplitude of the PGR to 10 auditory stimuli of 110 dB SPL were investigated in seven left-sided muscles. The size of the startle reflex, defined by the number of muscles activated by the acoustic stimulus and by the amplitude of the EMG response of the OO muscle as well, did not differ significantly between patients and controls. Median latencies of activity in the sternocleidomastoid (SC) (patients 80 ms; controls 54 ms) and the deltoid (DE) muscles (patients 113 ms; controls 69 ms) were prolonged significantly in PTSD compared to controls (P < 0.05). In the OO muscle, a late response (median latency in patients 308 ms; in controls 522 ms), probably the orienting reflex, was more frequently present in patients (56%) than in controls (12%). In patients, the mean PGR was enlarged compared to controls (P < 0.05). The size of the ASR response is not enlarged in PTSD patients. EMG latencies in the PTSD patients are prolonged in SC and DE muscles. The presence of a late response in the OO muscle discriminates between groups of PTSD patients with a history of startling and healthy controls. In addition, the autonomic response, i.e. the enlarged amplitude of the PGR can discriminate between these groups.

Soleus H-reflex tests and clinical signs of the upper motor neuron syndrome.

Soleus H-reflex tests are used for elucidating pathophysiological mechanisms in motor control. The cumulative vibratory inhibition of the soleus H-reflex, the ratio of the reflex to direct muscle potential (H to M ratio) and the recovery curve of the soleus H-reflex were studied in 38 patients with varying signs of the upper motor neuron syndrome for a possible relation with clinical features. The results were compared with those obtained from a group of healthy volunteers. The magnitude of vibratory inhibition decreased with increase of hypertonia. The H to M ratio increased as the activity of the tendon reflex was enhanced and correlated to a lesser degree with muscle tone. Both the H to M ratio and late facilitation of the soleus H-reflex recovery curve were elevated in clonus. The findings suggest that alterations in the results of soleus H-reflex tests relate to specific clinical features of the upper motor neuron syndrome. Possible pathophysiological implications are discussed.

Soleus H-reflex tests in spasticity and dystonia: A computerized analysis.

In 54 healthy individuals, and in 25 spastic and 7 dystonic subjects, soleus H-reflex vibratory inhibition, H M ratio, and homonymous recovery curves obtained at two stimulus intensity levels were investigated in the same subject. In spasticity, the most prominent changes consist of a diminution of the vibratory inhibition at stimulus intensities lower than needed for a maximum H-reflex and an increase in the H M ratio. These results suggest that presynaptic inhibition is reduced mainly at low-intensity levels and that excitability of motoneurons is increased. Recovery curves in spasticity do not show such significant changes as found for the recruitment curves. In dystonia, prominent changes occur in the late facilitatory phase of the recovery curve obtained at 0.5 H(max) stimulus intensity, suggesting increased interneuronal activity. Vibratory suppression may be diminished, but H M ratio is unaltered. A multivariate analysis was used to identify variables that discriminated between control, spastic, and dystonic subjects. The analysis yielded two canonical variables that are a linear combination of four H-reflex variables that contribute significantly to the group classification. Based on these two canonical variables, each group can be properly differentiated quantitatively.