"Tactile" stimulus intensity: information transmission by relay neurons in different trigeminal nuclei.

Comparison of the information transmitted about the intensity of a steady "tactile" stimulus applied to facial skin by single trigemino-thalamic neurons in nucleus oralis and nucleus caudalis indicates that little information loss occurs at the medial lemniscal synaptic relay (nucleus oralis), but that it is gross within the nucleus caudalis.

Brainstem auditory evoked potentials in postconcussion dizziness.

Twenty-seven patients with postconcussion dizziness following minor injury to the head or neck had brainstem auditory evoked potential studies from one day to eight months (median, 37 days) following injury. All patients were normal on clinical examination at the time of study. Three patients had one or more interpeak latencies prolonged beyond the 99% tolerance limit for normal control subjects. The group mean 1-3, 2-3, and 1-5 interpeak latencies were significantly prolonged. These findings indicate that minor head or neck injury with associated subjective symptomatology may be accompanied by objectively demonstrable brainstem dysfunction.

An intact nerve preparation for monitoring inputs from single joint afferent fibres.

A preparation is described that permits the monitoring of activity from individual joint afferent nerve fibres in an intact peripheral nerve of the cat. The joint nerve used was the medial articular nerve (MAN) that supplies the medial and anteromedial aspects of the knee joint. This nerve is sufficiently fine that if freed from nearby tissue over a length of 2-5 cm and placed over a platinum hook electrode it is possible to identify and monitor, from the intact nerve, the impulse activity from each group II joint afferent fibre activated by mechanical stimulation of the joint capsule. The signal-to-noise ratio exceeds 5:1 and in most cases was approximately 10:1. With this preparation it is now possible to examine the central actions and security of transmission at central synaptic targets for single, identified group II joint afferent fibres.

A method for the generation of complex vibrotactile stimuli.

A method is described utilizing computer-generated sine wave data and purpose-built hardware to generate a complex vibrotactile stimulus. Two sine waves of different frequency were summed to produce a complex waveform with two temporal components, a high frequency component and a low frequency beat component. The computer-generated data points for each of the two component sine waves were downloaded to two banks of static memory in a dual synchronous arbitrary function generator. The data points in memory were fed to two 12-bit digital-to-analogue converters which sent the two analogue sine wave signals to a summing amplifier where the two sine waves were added. This method provides a complex waveform that can be gated on and off, has a fixed frequency ratio of the component sine waves and no phase drift between the component waves. Addition of the separate sine waves in a summing amplifier allows for easy alteration of the amplitude ratio of the sine waves. The output of the summing amplifier is sent to a feedback controlled mechanical stimulator, thereby allowing the stimulus to be presented to the skin of human subjects and experimental animals.

Proprioceptive contributions to tactile identification of figures: dependence on figure size.

Studies on the recognition of objects or shapes explored by a hand or finger have concentrated on the relative merits of different methods of exploration--in particular, whether the exploring hand or finger is moved by the subject himself (active), is guided by an assistant (passive), or remains stationary with the shape being moved by an assistant (tactile). These factors, together with another variable--the size of the explored shape--were investigated in twelve normal adults whose task, without the aid of vision, was to explore and identify various shapes with the tip of the extended right index finger. Two series of shapes were used, a large (15 cm) and small (3 cm) series, both of which consisted of twelve shapes each being a variant of the letter 'S'. The shapes were outlined as rows of Braille-like dots on a flat surface. Exploration was also tested in the proprioceptive mode, in which the exploring hand was guided by an assistant around a shape which was simply drawn on the surface so as to give a minimum of tactile information. For neither large nor small shapes could we demonstrate differences between active, passive and proprioceptive exploration. For the small shapes, the active, passive and proprioceptive modes gave no advantage over purely tactile assessment. However, for the larger shapes, active, passive and proprioceptive modes allowed better identification than movement of the shape. Thus, purely cutaneous signals appear sufficient for optimal discrimination of small figures but proprioceptive signals, generated by movement, are needed for optimal discrimination of larger figures.

Specificity of tactile connections in neonatal cuneate nucleus.

In the neonatal kitten, cuneate neurones activated by tactile stimulation of the forelimb foot pads are divisible into 3 functional classes each of which appears to receive its glabrous skin input selectively from a single class of tactile receptors. Their properties suggest that the functionally specific patterns of tactile convergence characteristic of the adult cuneate nucleus are established by the time of birth.

A simple, accurate method for reproducing details of histological sections using a microfiche printer.

A rapid, inexpensive method is described for achieving accurate reproduction of histological sections. The method uses a microfiche reader-printer (for library use) which produces A4 size prints. Interchangeable lenses on the microfiche printer permit the magnification of the section to be varied over the range 6.6-72 times. Where large numbers of sections are involved the speed and low cost of the method offers considerable advantages over traditional hand tracing or photomicrography.

High gain transmission of single impulses through dorsal column nuclei of the cat.

Paired recordings were made in the cat from neurones of dorsal column nuclei and from intact pacinian sensory fibres of the hindlimb interosseous nerve. Direct evidence is presented for central neurones being driven by single impulses arriving over just one sensory nerve fibre. Transmission through this sensory relay appears to be optimized for the detection of minimal sensory inputs. Two mechanisms operate for the amplification of such inputs. First, individual sensory fibres can exert divergent, suprathreshold actions on multiple target neurones, and second, a single impulse coming over one input fibre can induce pairs or bursts of output spikes from its target neurones.

Representation of forelimb mechanoreceptors within the superior colliculus of the cat.

Forelimb mechanoreceptor representation within the superior colliculus was investigated using microelectrode recording in decerebrate or anaesthetized cats. Selective activation of different mechanoreceptive fibre classes supplying the distal forelimb revealed a poor representation of all three fibre classes (SA, PC and RA) that innervate the glabrous skin. Furthermore, there was no evidence for Pacinian (PC) input from the interosseous or wrist region. The tap stimuli which are often needed to activate the collicular neurones, may be effective, when applied to the distal limb, because of stimulus spread to more proximal sites, or as a result of the synchronous recruitment of multiple classes of afferent fibres.