Human perception of electrical stimulation on the surface of somatosensory cortex.

Recent advancement in electrocorticography (ECoG)-based brain-computer interface technology has sparked a new interest in providing somatosensory feedback using ECoG electrodes, i.e., cortical surface electrodes. We conducted a 28-day study of cortical surface stimulation in an individual with arm paralysis due to brachial plexus injury to examine the sensation produced by electrical stimulation of the somatosensory cortex. A high-density ECoG grid was implanted over the somatosensory and motor cortices. Stimulation through cortical surface electrodes over the somatosensory cortex successfully elicited arm and hand sensations in our participant with chronic paralysis. There were three key findings. First, the intensity of perceived sensation increased monotonically with both pulse amplitude and pulse frequency. Second, changing pulse width changed the type of sensation based on qualitative description provided by the human participant. Third, the participant could distinguish between stimulation applied to two neighboring cortical surface electrodes, 4.5 mm center-to-center distance, for three out of seven electrode pairs tested. Taken together, we found that it was possible to modulate sensation intensity, sensation type, and evoke sensations across a range of locations from the fingers to the upper arm using different stimulation electrodes even in an individual with chronic impairment of somatosensory function. These three features are essential to provide effective somatosensory feedback for neuroprosthetic applications.

Regenerated Sciatic Nerve Axons Stimulated through a Chronically Implanted Macro-Sieve Electrode.

Sieve electrodes provide a chronic interface for stimulating peripheral nerve axons. Yet, successful utilization requires robust axonal regeneration through the implanted electrode. The present study determined the effect of large transit zones in enhancing axonal regeneration and revealed an intimate neural interface with an implanted sieve electrode. Fabrication of the polyimide sieve electrodes employed sacrificial photolithography. The manufactured macro-sieve electrode (MSE) contained nine large transit zones with areas of ~0.285 mm2 surrounded by eight Pt-Ir metallized electrode sites. Prior to implantation, saline, or glial derived neurotropic factor (GDNF) was injected into nerve guidance silicone-conduits with or without a MSE. The MSE assembly or a nerve guidance conduit was implanted between transected ends of the sciatic nerve in adult male Lewis rats. At 3 months post-operation, fiber counts were similar through both implant types. Likewise, stimulation of nerves regenerated through a MSE or an open silicone conduit evoked comparable muscle forces. These results showed that nerve regeneration was comparable through MSE transit zones and an open conduit. GDNF had a minimal positive effect on the quality and morphology of fibers regenerating through the MSE; thus, the MSE may reduce reliance on GDNF to augment axonal regeneration. Selective stimulation of several individual muscles was achieved through monopolar stimulation of individual electrodes sites suggesting that the MSE might be an optimal platform for functional neuromuscular stimulation.

An implantable 64-channel neural interface with reconfigurable recording and stimulation.

Next generation implantable medical devices will have the potential to provide more precise and effective therapies through adaptive closed-loop controllers that combine sensing and stimulation across larger numbers of electrode channels. A major challenge in the design of such devices is balancing increased functionality and channel counts with the miniaturization required for implantation within small anatomical spaces. Customized therapies will require adaptive systems capable of tuning which channels are sensed and stimulated to overcome variability in patient-specific needs, surgical placement of electrodes, and chronic physiological responses. In order to address these challenges, we have designed a miniaturized implantable fully-reconfigurable front-end system that is integrated into the distal end of an 8-wire lead, enabling up to 64 electrodes to be dynamically configured for sensing and stimulation. Full reconfigurability is enabled by two custom 32×2 cross-point switch (CPS) matrix ASICs which can route any electrode to either an amplifier with reprogrammable bandwidth and integrated ADC or to one of two independent stimulation channels that can be driven through the lead. The 8-wire circuit includes a digital interface for robust communication as well as a charge-balanced powering scheme for enhanced safety. The system is encased in a hermetic package designed to fit within a 14 mm bur-hole in the skull for neuromodulation of the brain, but could easily be adapted to enhance therapies across a broad spectrum of applications.

Risk of obesity at 4 to 6 years of age among overweight or obese 18-month-olds: community-based cohort study.

OBJECTIVE: To determine whether high weight for length at the 18-month well-baby visit is predictive of overweight or obese body mass index (BMI) at the 4- to 6-year well-child visit. DESIGN: Retrospective cohort study using objective electronic medical record measurements. SETTING: Eighteen family practices forming a community family health organization in Peterborough, Ont. PARTICIPANTS: All children from the family health organization practices with at least 1 set of weight and length or height measurements at age 17 to 19 months and age 4 to 6 years (N=126). MAIN OUTCOME MEASURE: Relative risk (RR) of overweight BMI and RR of obese BMI at 4 to 6 years of age for normal versus overweight or obese 18-month-olds. RESULTS: Children who were either overweight or obese at their 18-month visits (n=37) were more than twice as likely to be obese at age 4 to 6 years than children who had healthy weights at 18 months were (n=89; RR=2.71, 95% CI 1.13 to 6.47). The subgroup of obese 18-month-olds (n=13) were at more than 3 times the risk of being obese at age 4 to 6 years than their healthy-weight-for-length counterparts (RR=3.42, 95% CI 1.20 to 9.78). Thirty-one percent of obese 18-month-olds were obese at 4 to 6 years and a further 31% were overweight. CONCLUSION: High weight for length at 18 months substantially increased a child's risk of being overweight or obese at 4 to 6 years of age. Most overweight and obese 18-month-olds in this study did not achieve healthy BMIs by 4 to 6 years of age. A brief glance at the 18-month weight-for-length chart can easily help identify these high-risk toddlers.

Cortical adaptation to a chronic micro-electrocorticographic brain computer interface.

Brain-computer interface (BCI) technology decodes neural signals in real time to control external devices. In this study, chronic epidural micro-electrocorticographic recordings were performed over primary motor (M1) and dorsal premotor (PMd) cortex of three macaque monkeys. The differential gamma-band amplitude (75-105 Hz) from two arbitrarily chosen 300 µm electrodes (one located over each cortical area) was used for closed-loop control of a one-dimensional BCI device. Each monkey rapidly learned over a period of days to successfully control the velocity of a computer cursor. While both cortical areas contributed to success on the BCI task, the control signals from M1 were consistently modulated more strongly than those from PMd. Additionally, we observe that gamma-band power during active BCI control is always above resting brain activity. This suggests that purposeful gamma-band modulation is an active process that is obtained through increased cortical activation.