Quantitative input-output relationships between human soleus muscle spindle afferents and motoneurons.

A method is described that, for the first time, allows instantaneous estimation of the Ia fiber input to human soleus motoneurons following electrical stimulation of the tibial nerve. The basis of the method is to determine the thresholds of the most and least excitable 1a fibers to electrical stimulation, and to treat the intervening thresholds as having a normal distribution about the mean; the validity of this approach is discussed. It was found that, for the same Ia fiber input, the percentage of soleus motoneurons contributing to the H (Hoffmann)-reflex differed considerably among subjects; when the results were pooled, however, there was an approximately linear relationship between Ia input and motoneuron output.

Can cross-talk occur in human myelinated nerve fibers?

Introduction: The possibility that impulse cross-talk can occur between myelinated human nerve fibers was explored.

Methods: Instances of impulse conduction without decrement were found, and published recordings of compound action potentials of functionally homogeneous fibers were scrutinized.

Results: Both analytical approaches yielded results consistent with cross-talk occurring in some nerves after electrical stimulation.

Hypothesis: Hughlings Jackson and presynaptic inhibition: is there a big picture?

Presynaptic inhibition is a very powerful inhibitory mechanism and, despite many detailed studies, its purpose is still only partially understood. One accepted function is that, by reducing afferent inflow to the spinal cord and brainstem, the tonic level of presynaptic inhibition prevents sensory systems from being overloaded. A corollary of this function is that much of the incoming sensory data from peripheral receptors must be redundant, and this conclusion is reinforced by observations on patients with sensory neuropathies or congenital obstetric palsy in whom normal sensation may be preserved despite loss of sensory fibers.

The Migraine Aura: A Problem for Vision Theory?

The scintillating zigzag pattern that a migraine patient may see as an illusion before the onset of headache offers a unique investigative approach to visual mechanisms. The likeliest interpretation of these zigzags is that they are the spontaneous discharges of the orientation-selective neurons first described in the striate cortex by Hubel and Wiesel (Hubel DH, Wiesel TN. Receptive fields, binocular interaction and functional architecture in the cat's visual cortex.

Transcranial Magnetic Stimulation in Migraine: A New Therapy and New Insights into Pathogenesis.

Transcranial magnetic stimulation (TMS) was first found to be effective in acute migraine 12 years ago, and subsequent studies have confirmed this benefit in approximately two -thirds of treated patients. High response rate, ease of application, and freedom from adverse effects combine to make TMS a natural front-line treatment for migraine, and its use should therefore be encouraged. In relation to the pathogenesis of migraine, the prompt relief of symptoms often observed with TMS is considered incompatible with an underlying neuroinflammatory process and with spreading depression as a cause of aura.

Cortical spreading depression in migraine-time to reconsider?

New evidence concerning the pathophysiology of migraine has come from the results of therapeutic transcranial magnetic stimulation (tTMS). The instantaneous responses to single pulses applied during the aura or headache phase, together with a number of other observations, make it unlikely that cortical spreading depression is involved in migraine. tTMS is considered to act by abolishing abnormal impulse activity in cortical pyramidal neurons and a suggestion is made as to how this activity could arise.

Tendon reflexes elicited using a computer controlled linear motor tendon hammer.

We present a novel instrumentation system for studying tendon and spinal reflexes using a commercial linear servo-motor as a precisely controlled tendon hammer. The system uses a LabVIEW-based program to both control electrical or mechanical stimuli and record and measure the resulting M and H waves. The hammer can deliver tendon taps with selected velocities, durations, frequencies and excursions.

Speculations surrounding a spinal reflex.

A method has been developed for measuring the Ia fibre input/motoneurone output relationship for the soleus H-reflex in healthy human volunteers. The shift in the relationship during weak toe extension, and in some subjects during weak plantar flexion, indicates the imposition of an inhibitory mechanism, presumably presynaptic. From these observations, and others previously made on long-loop reflexes, it is argued that the inhibitory mechanism may have evolved to suppress unwanted information from the periphery, not only during movement but in the resting state, and that this development was a necessary accompaniment of encephalisation.

Evaluation of therapeutic electrical stimulation to improve muscle strength and function in children with types II/III spinal muscular atrophy.

The study aimed to evaluate the effect of low-intensity night-time therapeutic electrical stimulation (TES) on arm strength and function in children with intermediate type spinal muscular atrophy (SMA). The design was a randomized controlled trial with a 6-month baseline control period. Children were evaluated at baseline, 6, and 12 months.