Transfer of information by BMI.

Brain machine interfaces (BMI) have become important in systems neuroscience with the goal to restore motor function in paralyzed patients. We assess the current ability of BMI devices to move objects. The topics discussed include: (1) the bits of information generated by a BMI signal, (2) the limitations of including more neurons for generating a BMI signal, (3) the superiority of a BMI signal using single cells versus electroencephalography, (4) plasticity and BMI, (5) the selection of a neural code for generating BMI, (6) the suppression of body movements during BMI, and (7) the role of vision in BMI. We conclude that further research on understanding how the brain generates movement is necessary before BMI can become a reasonable option for paralyzed patients.

Two-photon imaging and the activation of cortical neurons.

Based on two-photon calcium imaging, Histed et al. (2009) concluded that electrical microstimulation of cortical tissue in mammals activates a sparse and distributed population of neurons. This work has been cited by many as proof that electrical microstimulation is nonfocal, which means it may lack the precision needed for applications in neuroprosthetics. We affirm that the generation of stimulation-evoked behaviour is based primarily on the orthodromic conduction of signals originating mainly from the deepest layers of cortex, while the work of Histed et al. is effectively limited to investigating the antidromic activation of lateral projection neurons of the superficial cortex. The apparent sparse activation is a consequence of the pattern of axonal projections based on activating a volume of axons while imaging cell bodies transecting a single plane through the cortex. This creates the false impression that the distribution of activated neurons is sparse and nonfocal. We recommend how two-photon calcium imaging, which is superb for the study of individual and groups of neurons, might be more effectively used to ascertain how electrical stimulation affects the brains of mammals. This is a timely topic since investigators are using electrical microstimulation in animals to develop prosthetic devices to restore sensory and motor functions in disabled patients.

Direct and indirect activation of cortical neurons by electrical microstimulation.

Electrical microstimulation has been used to elucidate cortical function. This review discusses neuronal excitability and effective current spread estimated by using three different methods: 1) single-cell recording, 2) behavioral methods, and 3) functional magnetic resonance imaging (fMRI). The excitability properties of the stimulated elements in neocortex obtained using these methods were found to be comparable. These properties suggested that microstimulation activates the most excitable elements in cortex, that is, by and large the fibers of the pyramidal cells. Effective current spread within neocortex was found to be greater when measured with fMRI compared with measures based on single-cell recording or behavioral methods. The spread of activity based on behavioral methods is in close agreement with the spread based on the direct activation of neurons (as opposed to those activated synaptically). We argue that the greater activation with imaging is attributed to transynaptic spread, which includes subthreshold activation of sites connected to the site of stimulation. The definition of effective current spread therefore depends on the neural event being measured.

Phosphene induction and the generation of saccadic eye movements by striate cortex.

The purpose of this review is to critically examine phosphene induction and saccadic eye movement generation by electrical microstimulation of striate cortex (area V1) in humans and monkeys. The following issues are addressed: 1) Properties of electrical stimulation as they pertain to the activation of V1 elements; 2) the induction of phosphenes in sighted and blind human subjects elicited by electrical stimulation using various stimulation parameters and electrode types; 3) the induction of phosphenes with electrical microstimulation of V1 in monkeys; 4) the generation of saccadic eye movements with electrical microstimulation of V1 in monkeys; and 5) the tasks involved for the development of a cortical visual prosthesis for the blind. In this review it is concluded that electrical microstimulation of area V1 in trained monkeys can be used to accelerate the development of an effective prosthetic device for the blind.

Effects of training on saccadic eye movements elicited electrically from the frontal cortex of monkeys.

It has been reported that training affects motor responses evoked electrically from the dorsomedial frontal cortex (DMFC). Once a monkey had been trained to generate visually-guided saccadic eye movements of a particular size and direction, electrical stimulation of the DMFC elicited saccades of only that size and direction [7]. The current study re-investigates this finding. Monkeys were trained to produce saccadic eye movements to a visual target. After training, electrical stimulation was delivered to the DMFC. It was found that stimulation of the DMFC always evoked saccadic eye movements of the same size and direction before and after training, such that training had little effect on the responses evoked electrically from the DMFC. Differences between the current results and previous results have disclosed new clues as to how the DMFC might be modulated by learning.

Diabetes in urban African Americans: assessment of diabetes-specific locus of control in patients with type 2 diabetes.

PURPOSE: This study was conducted to examine the applicability and relationship to glycemic control of the Diabetes Locus of Control (DLC) Scales in a low-literacy, economically deprived, African American population with type 2 diabetes. METHODS: The DLC Scales were administered orally to African American patients with type 2 diabetes who had been referred to the diabetes unit of a large urban public hospital. Reliability, interscale correlations, and associations with patient characteristics were compared with those originally obtained for a better educated, predominately Caucasian population. RESULTS: The structure and correlates of the DLC Scales in the African American population were more similar than different from those originally obtained from a primarily well-educated, Caucasian population. However, comprehension of some items was difficult for up to 10% of the low-literacy population. A significant relationship was found between belief in chance and both glycemic control at the 6-month follow-up and the change in glycemic control over time. CONCLUSIONS: Although the DLC Scales operate similarly in an urban African American population with limited education, further modification is needed to enhance the prediction of glycemic control and provide direction for developing targeted interventions.

Eye fields in the frontal lobes of primates.

Two eye fields have been identified in the frontal lobes of primates: one is situated dorsomedially within the frontal cortex and will be referred to as the eye field within the dorsomedial frontal cortex (DMFC); the other resides dorsolaterally within the frontal cortex and is commonly referred to as the frontal eye field (FEF). This review documents the similarities and differences between these eye fields. Although the DMFC and FEF are both active during the execution of saccadic and smooth pursuit eye movements, the FEF is more dedicated to these functions. Lesions of DMFC minimally affect the production of most types of saccadic eye movements and have no effect on the execution of smooth pursuit eye movements. In contrast, lesions of the FEF produce deficits in generating saccades to briefly presented targets, in the production of saccades to two or more sequentially presented targets, in the selection of simultaneously presented targets, and in the execution of smooth pursuit eye movements. For the most part, these deficits are prevalent in both monkeys and humans. Single-unit recording experiments have shown that the DMFC contains neurons that mediate both limb and eye movements, whereas the FEF seems to be involved in the execution of eye movements only. Imaging experiments conducted on humans have corroborated these findings. A feature that distinguishes the DMFC from the FEF is that the DMFC contains a somatotopic map with eyes represented rostrally and hindlimbs represented caudally; the FEF has no such topography. Furthermore, experiments have revealed that the DMFC tends to contain a craniotopic (i.e., head-centered) code for the execution of saccadic eye movements, whereas the FEF contains a retinotopic (i.e., eye-centered) code for the elicitation of saccades. Imaging and unit recording data suggest that the DMFC is more involved in the learning of new tasks than is the FEF. Also with continued training on behavioural tasks the responsivity of the DMFC tends to drop. Accordingly, the DMFC is more involved in learning operations whereas the FEF is more specialized for the execution of saccadic and smooth pursuit eye movements.

Behavioural conditions affecting saccadic eye movements elicited electrically from the frontal lobes of primates.

We assessed the effects of varying the time at which electrical stimulation was delivered to the dorsomedial frontal cortex (DMFC) and the frontal eye fields (FEF) relative to the onset of a visual target. Monkeys were required to fixate the visual target to obtain a drop of apple juice as reward. We found that the probability of eliciting saccades increased with increases in the delay of electrical stimulation relative to target onset. Also, the current threshold to evoke saccades decreased as electrical stimulation was delivered later following target onset. There were major differences in the magnitude of this effect with stimulation of the DMFC versus the FEF. The current threshold to evoke saccades from the DMFC was 16 times greater when electrical stimulation was delivered 200 ms after target onset as compared to when it was delayed 200 ms after target offset. In contrast, the current threshold to evoke saccades from the FEFs was only three times greater when stimulation was delivered under similar conditions. These results suggest that the FEF are more closely connected with the saccade generator for the execution of saccadic eye movements than is the DMFC, even though both regions have direct projections to brainstem oculomotor centres.

Saccades induced electrically from the dorsomedial frontal cortex: evidence for a head-centered representation.

The amplitude and direction of saccadic eye movements evoked electrically from the dorsomedial frontal cortex (DMFC) of monkeys vary with starting eye position. This observation has been used to argue that the DMFC codes saccadic eye movements in head-centered coordinates. Whether the amplitude and direction of the evoked saccades are also affected by changes in head position has never been demonstrated. Such a result would argue against a head-centered representation, and instead would suggest a representation anchored to another body part. Tests were conducted on rhesus monkeys to determine whether changing the position of the head with respect to the trunk or changing the position of the head with respect to the gravitational axis alters saccadic parameters. The amplitude and direction of saccadic eye movements remained invariant to such manipulations. These findings confirm the claim that the DMFC encodes saccadic eye movements in head-centered coordinates.

Third-trimester biparietal diameter as a predictor of fetal lung maturity.

The major fetal risk associated with elective delivery is unexpected fetal lung immaturity and the development of hyaline membrane disease soon after birth. Prior to elective vaginal or abdominal delivery it has become standard obstetric practice to predict fetal lung maturity by the analysis of amniotic fluid obtained by amniocentesis or vaginal pool sample following preterm rupture of membranes. A correlation between third-trimester fetal biparietal diameter and the lecithin/sphingomyelin (L/S) ratio has been established by several investigators. In order to determine if a threshold BPD could be consistently correlated with fetal lung maturity, we retrospectively examined the hospital and laboratory records of a group of 115 nondiabetic parturients in whom BPD measurements and amniotic fluid analysis for L/S ratio had been performed for various clinical indications. A threshold BPD of greater than or equal to 9.2 cm in all parturients who underwent elective repeat cesarean delivery was associated with no hyaline membrane disease (HMD). Two of the three neonates who developed HMD had mature L/S ratios but were products of pregnancies complicated by third-trimester hemorrhage. A review of our present data suggests that about one-third of clinically-indicated amniocenteses in the absence of maternal diabetes or third-trimester hemorrhage could potentially be avoided without adverse neonatal impact. Possible therapeutic application of this finding requires further prospective study.