Medial temporal lobe functional connectivity predicts stimulation-induced theta power.

Focal electrical stimulation of the brain incites a cascade of neural activity that propagates from the stimulated region to both nearby and remote areas, offering the potential to control the activity of brain networks. Understanding how exogenous electrical signals perturb such networks in humans is key to its clinical translation. To investigate this, we applied electrical stimulation to subregions of the medial temporal lobe in 26 neurosurgical patients fitted with indwelling electrodes. Networks of low-frequency (5-13 Hz) spectral coherence predicted stimulation-evoked increases in theta (5-8 Hz) power, particularly when stimulation was applied in or adjacent to white matter. Stimulation tended to decrease power in the high-frequency broadband (HFB; 50-200 Hz) range, and these modulations were correlated with HFB-based networks in a subset of subjects. Our results demonstrate that functional connectivity is predictive of causal changes in the brain, capturing evoked activity across brain regions and frequency bands.

Widespread theta synchrony and high-frequency desynchronization underlies enhanced cognition.

The idea that synchronous neural activity underlies cognition has driven an extensive body of research in human and animal neuroscience. Yet, insufficient data on intracranial electrical connectivity has precluded a direct test of this hypothesis in a whole-brain setting. Through the lens of memory encoding and retrieval processes, we construct whole-brain connectivity maps of fast gamma (30-100 Hz) and slow theta (3-8 Hz) spectral neural activity, based on data from 294 neurosurgical patients fitted with indwelling electrodes. Here we report that gamma networks desynchronize and theta networks synchronize during encoding and retrieval. Furthermore, for nearly all brain regions we studied, gamma power rises as that region desynchronizes with gamma activity elsewhere in the brain, establishing gamma as a largely asynchronous phenomenon. The abundant phenomenon of theta synchrony is positively correlated with a brain region's gamma power, suggesting a predominant low-frequency mechanism for inter-regional communication.

Nutritional rickets in young Nigerian children in the Sahel savanna.

OBJECTIVES: To determine the prevalence of clinical and biochemical rickets in an under-five out-patient population, relate the prevalence of biochemical rickets (BR) to the sociocultural characteristics of families and determine the response of nutritional rickets to vitamin D therapy. DESIGN: Prospective cross-sectional and retrospective case-series surveys. SETTING: Paediatric general out-patient and consultant clinics. SUBJECTS: One hundred and ninety eight out-patients and twenty two patients aged >1 to 60 months treated for nutritional rickets. INTERVENTIONS: Clinical examination, interview with mothers and determination of biochemical abnormalities of under-fives and management of patients with rickets using stosstherapy. MAIN OUTCOME MEASURES: Prevalence of BR and response to stosstherapy. RESULTS: Eight (4%) patients in the survey had clinical and biochemical rickets while 33 (17%) had biochemical rickets only; 92 (47%) other patients had isolated hypocalcaemia and/or hypophosphataemia. The prevalence of BR was higher in males (p <0.05), and increased with age (p <0.001). The prevalence was lower in families who were indigenous to the area (p <0.05), children of Moslem families (p <0.05) and children whose mothers were full-time housewives, unskilled or traders (p <0.01), and who lacked any formal western education (p = 0.157). Three of the seven evaluable patients who received stosstherapy responded late. CONCLUSION: The results support the hypothesis that deficiency or reduced availability of dietary calcium may be of at least equal importance with vitamin D deficiency in the aetiology of nutritional rickets in the Sahel savanna.

Hypoglycaemia: a major biochemical complication in eclampsia- its risk factors and prognostic value.

In this two year prospective study, random blood glucose levels were determined in 52 eclamptic patients and 38 controls, at the University of Maiduguri Teaching Hospital and Specialist Hospitals in Maiduguri, Nigeria. Eclamptic mothers had lower glucose levels (mean value = 3.5 mmol/l) than controls (mean value = 6.8 mmol/l) (P < 0.001). Nineteen eclamptics (36.5%) had hypoglycaemic glucose levels (mean value = 2.3 mmol/l). These values returned to normal following intravenous administration of dextrose. Risk factors for hypoglycaemia identified in these mothers included lack of antenatal care, unsupervised labour at home, labour lasting more than 14 hours, obstructed labour, maternal hyperpyrexia, convulsions four or more times, deranged liver function especially HELLP syndrome (syndrome of haemolysis, elevated liver enzymes and low platelet count), poor energy supply in labour, low socio-economic class status and anaemia. A scoring panel derived from these risk factors was tested on a separate group of 48 eclamptics and this was found to be 96% sensitive. Infusion of 50% dextrose reversed coma in seven of eight comatose eclamptics and corrected fetal heart rate irregularities in 13 of 15 hypoglycaemic eclamptics. Seven of nine patients who suffered from posteclamptic psychosis had hypoglycaemic glucose levels. Three mothers with hypoglycaemia and HELLP syndrome died after developing hyperglycaemia following infusions of 50% and 10% dextrose. Hypoglycaemia should be considered a major biochemical complication of eclampsia. Its risk should be identified and its treatment be considered in the protocol of the management of eclamptics.