A charge-metering method for voltage-mode neural stimulation

AbstractElectrical neural stimulation is the technique used to modulate neural activity by inducing an instantaneous charge imbalance. This is typically achieved by injecting a constant current and controlling the stimulation time. However, constant voltage stimulation is found to be more energy-efficient although it is challenging to control the amount of charge delivered. This paper presents a novel, fully integrated circuit for facilitating charge-metering in constant voltage stimulation. It utilises two complementary stimulation paths. Each path includes a small capacitor, a comparator and a counter. They form a mixed-signal integrator that integrates the stimulation current onto the capacitor while monitoring its voltage against a threshold using the comparator. The pulses from the comparator are used to increment the counter and reset the capacitor. Therefore, by knowing the value of the capacitor, threshold voltage and output of the counter, the quantity of charge delivered can be calculated. The system has been fabricated in 0.18μm CMOS technology, occupying a total active area of 339μm×110μm. Experimental results were taken using: (1) a resistor–capacitor EEI model and (2) platinum electrodes with ringer solution. The viability of this method in recruiting action potentials has been demonstrated using a cuff electrode with Xenopus sciatic nerve. For a 10nC target charge delivery, the results of (2) show a charge delivery error of 3.4% and a typical residual charge of 77.19pC without passive charge recycling. The total power consumption is 45μW. The performance is comparable with other publications. Therefore, the proposed stimulation method can be used as a new approach for neural stimulation

Case against diagnosing developmental language disorder by default: A single case study of acquired aphasia associated with convulsive disorder

The aim of this article is to inform the diagnostic kwnowledge base for professionals working in the field of language disorders when classic symptoms, characteristics and sequences are not found. The information reveals the risk of diagnosis with a developmental language disorder (DLD) by default when no underlying cause can be readily identified. Diagnostic history was obtained retrospectively from parental interview and contemporary professional reports. Ten years of diagnostic investigations are reported in time-related sequences. Due to variability and inconsistency in his receptive and expressive language skills, the case-study participant (David) was unable to be reliably assessed using standardized tests. Therefore, numerical data and statistical analyses are not reported. The report, however, details the multitude of investigations and opinions obtained before a definitive diagnosis of acquired aphasia associated with convulsive disorder (AACD) was made. Davidĝ€™s history cautions that diagnosing developmental language disorder when no underlying cause for the impairment is recognized may allow underlying disorders and conditions to progress. Clinicians faced with a child whose skill profile is not consistent with a specific diagnosis or expected criteria are thus advised to pursue a definitive diagnosis rather than accept one by default