Detailed clinical assessment of neurological function in symptomatic shipyard workers

Forty eight patients with extensive occupational exposure to pneumatic grinding tools were evaluated at a university sponsored occupational health clinic. All patients were interviewed and examined by a physician and assessed neurologically with standard clinical, functional motor, quantitative vibrotactile, and electrodiagnostic tests. Sensorineural symptoms were nearly universal; 47 patients (98%) reported numbness and tingling of the hands and fingers. Among clinical tests, two point discrimination and 30 Hz vibration perception were most frequently abnormal. In order to evaluate associations between quantitative test results and sensorineural symptoms, patients were stratified into two groups of symptom severity according to a consensus sensorineural staging system. The tests that discriminated best between the groups of more and less symptomatic patients were hand strength dynamometry, and vibrotactile thresholds. Age standardised 120 Hz vibrotactile thresholds were significantly raised in digit II in 41% of hand measurements. Nerve conduction studies were neither significantly different between more and less symptomatic groups nor correlated with clinical and quantitative sensory tests. Twenty five per cent of the patients had slowing of sensory conduction velocities in the median nerve at the wrist (less than 48 m/s). Of this subset of patients only two showed abnormal slowing of the median nerve distal to the wrist, but half also showed ulnar nerve slowing (less than 47 m/s).This observation highlights the difficulty of differentiating median nerve entrapment from diffuse distal neuropathy in workers exposed to vibration and points to the need for concomitant quantitative sensory and functional motor assessment.     

Caffeine restores regional brain activation in acute hypoglycaemia in healthy volunteers.

AIMS: Caffeine enhances counterregulatory responses to acute hypoglycaemia. Our aim was to explore its effects on cortical function, which are not known at present. METHODS: Regional brain activation during performance of the four-choice reaction time (4CRT) at different levels of complexity was measured using functional magnetic resonance imaging (fMRI) at euglycaemia (5 mmol/l) and hypoglycaemia (2.6 mmol/l) in the presence and absence of caffeine in six healthy right-handed men. RESULTS: During hypoglycaemia, caffeine enhanced adrenaline responses to hypoglycaemia (2.5 +/- 0.7 nmol/l to 4.0 +/- 1.0 nmol/l, P = 0.01) and restored the brain activation response to the non-cued 4CRT, the linear increases in regional brain activation associated with increased task complexity and the ability to respond to a cue that were lost in hypoglycaemia alone. CONCLUSIONS: Caffeine can sustain regional brain activation patterns lost in acute hypoglycaemia, with some restoration of cortical function and enhanced adrenaline responsiveness. A methodology has been established that may help in the development of therapies to protect against severe hypoglycaemia in insulin therapy for patients with diabetes and problematic hypoglycaemia.     

Heterotopic heart transplants in Biomphalaria glabrata (mollusca: pulmonata). Fate of congeneric xenografts

Hearts were implanted heterotopically into the hemocoel of NIH albino Biomphalaria glabrata from three xenogeneic donor snails, including two New World (B. obstructa, B. tenagophila) and one Old World (B. alexandrina) species, as well as from wild type allogeneic donors. Recipients were examined histologically at 1, 3, 7, 10, 15, 30, 60, 120, and 180 days postimplantation (PI). Grafts from all four donor species were temporarily infiltrated by recipient hemocytes at early intervals PI and in most instances also became encapsulated. Furthermore, the grafts subsequently showed histopathological alterations and abnormal heartbeat relative to preimplantation controls. However, hemocytic reactions eventually subsided, the implants remained structurally intact, and implant myocardial cells both maintained high levels of intracellular glycogen and continued to contract rhythmically for 6 months. No major differences occurred in fates among different xenografts, or between xenografts and allografts. Our observations of prolonged xenograft survival differ from those of previous investigators, most of whom have reported rapid destruction of implanted xenogeneic tissues in molluscs.     

Response amplification in sensory-specific cortices during crossmodal binding

Integrating information across the senses can enhance our ability to detect and classify stimuli in the environment. For example, auditory speech perception is substantially improved when the speaker's face is visible. In an fMRI study designed to investigate the neural mechanisms underlying these crossmodal behavioural gains, bimodal (audio-visual) speech was contrasted against both unimodal (auditory and visual) components. Significant response enhancements in auditory (BA 41/42) and visual (V5) cortices were detected during bimodal stimulation. This effect was found to be specific to semantically congruent crossmodal inputs. These data suggest that the perceptual improvements effected by synthesizing matched multisensory inputs are realised by reciprocal amplification of the signal intensity in participating unimodal cortices.     

Recovery from optic neuritis is associated with a change in the distribution of cerebral response to visual stimulation: a functional magnetic resonance imaging study

OBJECTIVES: Recovery to normal or near normal visual acuity is usual after acute demyelinating optic neuritis, despite the frequent persistence of conduction abnormalities as evidenced by the visual evoked potential (VEP). This raises the possibility that cortical adaptation to a persistently abnormal input contributes to the recovery process. The objective of this study was to investigate the pattern of cerebral response to a simple visual stimulus in recovered patients in comparison to normal subjects. METHODS: Functional magnetic resonance imaging (fMRI) was used to study the brain activation pattern induced by a periodic monocular 8Hz photic stimulus in seven patients who had recovered from a single episode of acute unilateral optic neuritis, and in seven normal controls. VEPs and structural optic nerve MRI were performed on patients. RESULTS: Stimulation of either eye in controls activated only the occipital visual cortex. However, in patients, stimulation of the recovered eye also induced extensive activation in other areas including the insula-claustrum, lateral temporal and posterior parietal cortices, and thalamus; stimulation of the clinically unaffected eye activated visual cortex and right insula-claustrum only. The volume of extraoccipital activation in patients was strongly correlated with VEP latency (r = 0.71, p = 0.005). CONCLUSIONS: The extraoccipital areas that were activated in patients all have extensive visual connections, and some have been proposed as sites of multimodal sensory integration. The results indicate a functional reorganisation of the cerebral response to simple visual stimuli after optic neuritis that may represent an adaptive response to a persistently abnormal input. Whether this is a necessary part of the recovery process remains to be determined.     

The neural correlates of orienting: an integration of fMRI and skin conductance orienting

In fMRI studies, the averaging of neural activity across multiple trials might obscure important psychophysiological subprocesses. The orienting response (OR) is a distinctive subprocess signalling the active orientation of attention towards potentially significant events. We sought to elucidate fMRI activity associated with visual stimuli that did or did not evoke simultaneously recorded electrodermal ORs (using customised skin conductance recording). 'With-OR' stimuli were associated with significant activity in the hippocampus, anterior cingulate and ventromedial prefrontal cortex. Averaged analysis revealed activity only in the expected visual circuits. Our results suggest that potentially significant stimuli (with-OR) activate different functional networks to familiar (without-OR) stimuli, and that orienting may therefore be an informative subprocess to consider in cognitive fMRI studies.     

Lexical retrieval during fluent speech production: an fMRI study

We investigated the neural correlates of lexical retrieval during fluent speech production using fMRI. Blood oxygenation level dependent (BOLD) contrast was measured while subjects spoke about 7 Rorschach inkblots for 3 min each. Varying degrees of speech rate were elicited during each run. In a within-subject design, the number of words produced was correlated with the BOLD contrast in the two runs in each subject that showed the highest variance of speech output. The rate of articulation was positively correlated with activation in the left superior temporal (BA 22) and supramarginal (BA 39/ 40) gyri. The main negative correlations were in the fusiform gyri bilaterally (BA 19), the posterior cingulate (BA 30) and superior occipital gyrus (BA 19). Lexical retrieval during continuous language production engages areas in the left temporal and inferior parietal cortex. This pattern of activation differs from that evident during the generation of single words (verbal fluency), which is more associated with left prefrontal activation.