Investigation of liver-targeted peripheral focused ultrasound stimulation (pFUS) and its effect on glucose homeostasis and insulin resistance in type 2 diabetes mellitus: a proof of concept, phase 1 trial

BACKGROUND

Mechanical waves produced by ultrasound pulses have been shown to activate mechanosensitive ion channels and modulate peripheral nerves. However, while peripheral ultrasound neuromodulation has been demonstrated in vitro and in pre-clinical models, there have been few reports of clinical tests.

AIM

We modified a diagnostic imaging system for ultrasound neuromodulation in human subjects. We report the first safety and feasibility outcomes in subjects with type 2 diabetes (T2D) mellitus and discuss these outcomes in relation to previous pre-clinical results.

DESIGN

The study was performed as an open label feasibility study to assess the effects of hepatic ultrasound (targeted to the porta hepatis) on glucometabolic parameters in subjects with T2D. Stimulation (peripheral focused ultrasound stimulation treatment) was performed for 3 days (i.e. 15 min per day), preceded by a baseline examination and followed by a 2-week observation period.

METHODS

Multiple metabolic assays were employed including measures of fasting glucose and insulin, insulin resistance and glucose metabolism. The safety and tolerability were also assessed by monitoring adverse events, changes in vital signs, electrocardiogram parameters and clinical laboratory measures.

RESULTS AND CONCLUSION

We report post-pFUS trends in several outcomes that were consistent with previous pre-clinical findings. Fasting insulin was lowered, resulting in a reduction of HOMA-IR scores (P-value 0.01; corrected Wilcoxon signed-rank test). Additional safety and exploratory markers demonstrated no device-related adverse impact of pFUS. Our findings demonstrate that pFUS represents a promising new treatment modality that could be used as a non-pharmaceutical adjunct or even alternative to current drug treatments in diabetes.

Inferior olive response to passive tactile and visual stimulation with variable interstimulus intervals

The unique anatomical and electrophysiological features of the inferior olive and its importance to cerebellar function have been recognized for decades. However, understanding the exact function of the inferior olive has been limited by the general lack of correlation between its neural activity and specific behavioral states. Electrophysiological studies in animals showed that the inferior olive response to sensory stimuli is generally invariant to stimulus properties but is enhanced by unexpected stimuli. Using functional magnetic resonance imaging in humans, we have shown that the inferior olive is activated when subjects performed a task requiring perception of visual stimuli with unpredictable timing (Xu et al. J Neurosci 26(22):5990-5995, 2006, Liu et al. J Neurophysiol 100(3):1557-1561, 2008). In the current study, subjects were scanned while passively perceiving visual and tactile stimuli that were rendered unpredictable by continuously varying interstimulus intervals (ISIs). Sequences of visual stimuli and tactile stimuli to the right hand were presented separately within the same scanning session. In addition to the activation of multiple areas in the cerebellar cortex consistent with previous imaging studies, the results show that both tactile and visual stimulation with variable ISIs were effective in activating the inferior olive. Together with our previous findings, the current results are consistent with the electrophysiological studies in animals and further support the view that the inferior olive and the climbing fiber system primarily convey the temporal information of sensory input regardless of the modality.

Specificity of inferior olive response to stimulus timing

The inferior olive is the sole source of the climbing fiber system, one of the two major afferent systems of the cerebellum; however, its exact role remains unknown. A longstanding hypothesis is that the inferior olive with its unique intrinsic rhythmic firing properties mediates motor timing. However, direct evidence linking the inferior olive to timing behavior has been difficult to demonstrate in animal or human studies likely due to the inhibition of inferior olive responses by self-produced movement. Here we used event-related functional magnetic resonance imaging (fMRI) and a perceptual task that dissociates the temporal from nontemporal attributes of sensory input. Subjects were asked to attend to rhythmically occurring identical visual stimuli and to detect a change in their timing, spatial orientation, or color. Inferior olive activation was seen only when perceiving a change in stimulus timing. These results are consistent with animal studies demonstrating that the inferior olive is especially sensitive to "unexpected" sensory events and further provide evidence supporting the specificity of the inferior olive response to stimulus timing. The results are consistent with the view that the inferior olive and the climbing fiber system mediate the encoding of temporal information required for both motor and nonmotor cognitive processes.

Selective impairments in implicit learning in Parkinson's disease

The basal ganglia are thought to participate in implicit sequence learning. However, the exact nature of this role has been difficult to determine in light of the conflicting evidence on implicit learning in subjects with Parkinson's disease (PD). We examined the performance of PD subjects using a modified form of the serial reaction time task, which ensured that learning remained implicit. Subjects with predominantly right-sided symptoms were trained on a 12-element sequence using the right hand. Although there was no evidence of sequence learning on the basis of response time savings, the subjects showed knowledge of the sequence when performance was assessed in terms of the number of errors made. This effect transferred to the left (untrained) hand as well. Thus, these data demonstrate that PD patients are not impaired at implicitly learning sequential order, but rather at the translation of sequence knowledge into rapid motor performance. Furthermore, the results suggest that the basal ganglia are not essential for implicit sequence learning in PD.

Neural correlates of encoding and expression in implicit sequence learning

In the domain of motor learning it has been difficult to separate the neural substrate of encoding from that of change in performance. Consequently, it has not been clear whether motor effector areas participate in learning or merely modulate changes in performance. Here, using a variant of the serial reaction time task that dissociated these two factors, we report that encoding during procedural motor learning does engage cortical motor areas and can be characterized by distinct early and late encoding phases. The highest correlation between activation and subsequent changes in motor performance was seen in the motor cortex during early encoding, and in the basal ganglia during the late encoding phase. Our results show that rapid encoding during procedural motor learning involves several distinct processes, and is represented primarily within motor system structures.

Probability detection mechanisms and motor learning

The automatic detection of patterns or regularities in the environment is central to certain forms of motor learning, which are largely procedural and implicit. The rules underlying the detection and use of probabilistic information in the perceptual-motor domain are largely unknown. We conducted two experiments involving a motor learning task with direct and crossed mapping of motor responses in which probabilities were present at the stimulus set level, the response set level, and at the level of stimulus-response (S-R) mapping. We manipulated only one level at a time, while controlling for the other two. The results show that probabilities were detected only when present at the S-R mapping and motor levels, but not at the perceptual one (experiment 1), unless the perceptual features have a dimensional overlap with the S-R mapping rule (experiment 2). The effects of probability detection were mostly facilitatory at the S-R mapping, both facilitatory and inhibitory at the perceptual level, and predominantly inhibitory at the response-set level. The facilitatory effects were based on learning the absolute frequencies first and transitional probabilities later (for the S-R mapping rule) or both types of information at the same time (for perceptual level), whereas the inhibitory effects were based on learning first the transitional probabilities. Our data suggest that both absolute frequencies and transitional probabilities are used in motor learning, but in different temporal orders, according to the probabilistic properties of the environment. The results support the idea that separate neural circuits may be involved in detecting absolute frequencies as compared to transitional probabilities.

Cerebellum activation associated with performance change but not motor learning

The issue of whether the cerebellum contributes to motor skill learning is controversial, principally because of the difficulty of separating the effects of motor learning from changes in performance. We performed a functional magnetic resonance imaging investigation during an implicit, motor sequence-learning task that was designed to separate these two processes. During the sequence-encoding phase, human participants performed a concurrent distractor task that served to suppress the performance changes associated with learning. Upon removal of the distractor, participants showed evidence of having learned. No cerebellar activation was associated with the learning phase, despite extensive involvement of other cortical and subcortical regions. There was, however, significant cerebellar activation during the expression of learning; thus, the cerebellum does not contribute to learning of the motor skill itself but is engaged primarily in the modification of performance.

Imaging tip formation in single-mode optical fibres

The formation of probe tips is a crucial step in all forms of scanning probe microscopy (SPM). In this work single-mode optical fibres are chemically etched in a variable temperature bath of etchant solution (HF acid buffered with ammonium fluoride) to produce tips for optical SPM. Tip evolution is monitored by prematurely truncating the etching process and imaging the tip end-structure using atomic force microscopy (AFM). In the case of a visible regime single-mode fibre the AFM images show a remarkable ring structure in the central cladding region and a tip structure in the core with a central depression; this serves to demonstrate the efficacy of chemical etching for converting compositional variation to three-dimensional topography. In the case of a standard, single-mode optical communications fibre the (projected) tip cone angle is assessed from AFM images in the early stages of tip formation. Values of the cone angle thus determined, for different etch conditions, are compared to those predicted by a model in which the independently determined core and cladding etch rates, and core diameter are the sole determinants of the final tip geometry. The model was devised in the context of etching multi-mode fibres and is shown to be valid here for single-mode fibres within the range of experimental accuracy and etch conditions examined.

The effect of stimulus-response compatibility on cortical motor activation

Stimulus-response compatibility (SRC) is a general term describing the relationship between a triggering stimulus and its associated motor response. The relationship between stimulus and response can be manipulated at the level of the set of stimulus and response characteristics (set-level) or at the level of the mapping between the individual elements of the stimulus and response sets (element-level). We used functional magnetic resonance imaging (fMRI) to investigate the effects of SRC on functional activation in cortical motor areas. Using behavioral tasks to separately evaluate set- and element-level compatibility, and their interaction, we measured the volume of functional activation in 11 cortical motor areas, in the anterior frontal cortex, and in the superior temporal lobe. Element-level compatibility effects were associated with significant activation in the pre-supplementary motor area (preSMA), the dorsal (PMd) and ventral (PMv) premotor areas, and the parietal areas (inferior, superior, intraparietal sulcus, precuneus). The activation was lateralized to the right hemisphere for most of the areas. Set-level compatibility effects resulted in significant activation in the inferior frontal gyri, anterior cingulate and cingulate motor areas, the PMd, PMv, preSMA, the parietal areas (inferior, superior, intraparietal sulcus, precuneus), and in the superior temporal lobe. Activation in the majority of these areas was lateralized to the left hemisphere. Finally, there was an interaction between set and element-level compatibility in the middle and superior frontal gyri, in an area co-extensive with the dorsolateral prefrontal cortex, suggesting that this area provided the neural substrate for common processing stages, such as working memory and attention, which are engaged when both levels of SRC are manipulated at once.

Effects of changes in experimental design on PET studies of isometric force

Based on single-cell recordings in primates, the relationship between neuronal activity and force magnitude is thought to be monotonic, at least for a subset of pyramidal cells in the motor cortex. Functional neuroimaging studies have also suggested a monotonic relationship between cerebral activation and force magnitude. In order to more precisely define this relationship and to characterize the activation pattern(s) associated with the modulation of static force, we studied 40 normal subjects using [(15)O]water PET and a simple visuomotor task-application of static force on a micro force sensor with the thumb and index finger of the right hand. When our experimental design did not produce the expected result (evidence of a relationship between cerebral activation and force magnitude in ten subjects), we made serial changes in the experimental protocol, including the addition of control (baseline) trials, and increased the number of subjects in an effort to increase our sensitivity to variations in force magnitude. We compared univariate and multivariate data-analytic strategies, but we relied on our multivariate results to elucidate the interaction of attentional and motor networks. We found that increasing the number of subjects from 10 to 20 resulted in an increase in statistical power and a more stable (i.e., more replicable) but qualitatively similar result, and that the inclusion of control trials in a 10-subject group did not enhance our ability to discern significant brain-behavior relationships. Our results suggest that sample sizes greater than 20 may be required to detect parametric variation in some instances and that failure to detect such variation may result from unanticipated neurobehavioral effects.

Choice and stimulus-response compatibility affect duration of response selection

In general, for movements to visual targets, response times increase with the number of possible response choices. However, this rule only seems to hold when an incompatibility exists between the stimulus and response, and is absent when stimulus and response are highly compatible (e.g., when reaching toward the location of the stimulus). Stimulus-response (S-R) compatibility can be manipulated either at the level of stimulus and response characteristics, or at the level of the mapping between elements of the stimulus and response sets. The current study was undertaken to determine the extent of the interaction between choice and each of these two levels of S-R compatibility. Subjects used a joystick to move a cursor in response to two, four or eight possible cues, with S-R compatibility manipulated along two dimensions (type of stimulus, and mapping between stimulus and response sets) in separate blocks of trials. Choice effects were absent when S-R relationships were highly compatible, moderate when incompatible in either of the two dimensions, and greatest when incompatible in both dimensions. These results indicate that choice affects response selection at each stage in the decoding of S-R relationships. Similar but smaller effects were seen for trials in which the stimulus was the same as that presented in the immediately preceding trial, suggesting that repeated stimulus-response transformations are faster and more efficient due to the priming effects of previous trials.

Effects of movement predictability on cortical motor activation

Humans have the ability to make motor responses to unpredictable visual stimuli, and do so as a matter of course on a daily basis. We used functional magnetic resonance imaging (fMRI) to examine the neural substrate of this behavior in six cortical motor areas. We found that five of these areas (premotor, cingulate, supplementary motor area, pre-supplementary motor area, and superior parietal lobule) showed increased activation in association with an unpredictable behavior compared to a predictable one; only the motor cortex remained unchanged. There was also a quantitative relation between the response time and functional activation in the premotor and cingulate cortex. There was less activation across all the motor areas with repetition of the motor tasks. With the exception of the pre-supplementary motor area, all areas were significantly lateralized, with a greater volume of activation in the hemisphere contralateral to the performing hand. In addition, a left hemisphere dominance was found in the activation of motor cortex and supplementary motor areas. Our results suggest that activation in motor areas is differentially and quantitatively related to higher order aspects of motor behavior such as movement predictability.

Functional activation in motor cortex reflects the direction and the degree of handedness

Handedness is the clearest example of behavioral lateralization in humans. It is not known whether the obvious asymmetry manifested by hand preference is associated with similar asymmetry in brain activation during movement. We examined the functional activation in cortical motor areas during movement of the dominant and nondominant hand in groups of right-handed and left-handed subjects and found that use of the dominant hand was associated with a greater volume of activation in the contralateral motor cortex. Furthermore, there was a separate relation between the degree of handedness and the extent of functional lateralization in the motor cortex. The patterns of functional activation associated with the direction and degree of handedness suggest that these aspects are independent and are coded separately in the brain.

Force and the motor cortex

The relation between the activity of cells in the motor cortex and static force has been studied extensively. Most studies have concentrated on the relation to the magnitude of force; this relation is more or less monotonic. The slope of the relation, however, shows considerable variation among different studies and seems to be inversely associated with the range of forces over which the cell activity has been studied. Cells in the motor cortex also show variation in activity with the direction of static force. When both the direction and the magnitude of static force are allowed to vary, a majority of cells show significant changes in activity with direction of force alone, an intermediate number relate to both direction and magnitude, while a small number relate purely to the magnitude. This suggests that the direction of static force can be controlled independently of its magnitude and that this directional signal is especially prominent in the motor cortex. In general, it has been more difficult to study the relations to dynamic force. There is a correlation between motor cortex cell activity and the rate of change of force. The direction of dynamic force is also an important determinant of cell activity. When both static and dynamic force output are required (for example, with arm movement in the presence of gravity) it is the dynamic signal that is most clearly reflected in motor cortex activity. The relations between motor cortex activity and static or dynamic force are not invariant, but may be modified by the behavioral context of the motor output.

Multi-slice perfusion-based functional MRI using the FAIR technique: comparison of CBF and BOLD effects

Perfusion-weighted imaging techniques employing blood water protons as an endogenous tracer have poor temporal resolution because each image should be acquired with an adequate spin 'tagging' time. Thus, perfusion-based functional magnetic resonance imaging studies are typically performed on a single slice. To alleviate this problem, a multi-slice flow-sensitive alternating inversion recovery technique has been developed. Following a single inversion pulse and a delay time, multi-slice echo-planar images are acquired sequentially without any additional inter-image delay. Thus, the temporal resolution of multi-slice FAIR is almost identical to that of single slice techniques. The theoretical background for multi-slice FAIR is described in detail. The multi-slice FAIR technique has been successfully applied to obtain three-slice cerebral blood flow based functional images during motor tasks. The relative CBF change in the contralateral motor/sensory area during unilateral thumb-digit opposition is 45.0+/-12.2% (n=9), while the blood oxygenation level dependent signal change is 1.5+/-0.4 SD%. Relative changes of the oxygen consumption rate can be estimated from CBF and BOLD changes using FAIR. The BOLD signal change is not correlated with the relative CBF increase, and thus caution should be exercised when interpreting the BOLD change as a quantitative index of the CBF change, especially in inter-subject comparisons.

Force and the motor cortex

The relation between the activity of cells in the motor cortex and static force has been studied extensively. Most studies have concentrated on the relation to the magnitude of force; this relation is more or less monotonic. The slope of the relation, however, shows considerable variation among different studies and seems to be inversely associated with the range of forces over which the cell activity has been studied. Cells in the motor cortex also show variation in activity with the direction of static force. When both the direction and the magnitude of static force are allowed to vary, a majority of cells show significant changes in activity with direction of force alone, an intermediate number relate to both direction and magnitude, while a small number relate purely to the magnitude. This suggests that the direction of static force can be controlled independently of its magnitude and that this directional signal is especially prominent in the motor cortex. In general, it has been more difficult to study the relations to dynamic force. There is a correlation between motor cortex cell activity and the rate of change of force. The direction of dynamic force is also an important determinant of cell activity. When both static and dynamic force output are required (for example, with arm movement in the presence of gravity) it is the dynamic signal that is most clearly reflected in motor cortex activity. The relations between motor cortex activity and static or dynamic force are not invariant, but may be modified by the behavioral context of the motor output.

Microstimulation of primate motor thalamus: somatotopic organization and differential distribution of evoked motor responses among subnuclei

1. The functional organization of motor responses to microstimulation throughout the primate "motor" thalamus including nucleus ventralis lateralis, pars oralis (VLo); nucleus ventralis posterior lateralis, pars oralis (VPLo); nucleus ventralis lateralis, pars caudalis (VLc); and portions of ventralis anterior (VA) and area X, was systematically studied in awake monkeys. A total of 2,021 sites were examined for their response to microstimulation. Of these, 1,123 were histologically verified as to their location within the motor thalamus. At or near each site, isolated neurons were examined for their responses to somatosensory examination and active movement (n = 1,272). This study was carried out as part of a larger study examining the responses of neurons in the motor thalamus to somatosensory examination, torque-induced limb perturbations, and active movement in a visuomotor step-tracking task. 2. Microstimulation at < or = 40 microA evoked movements in the contralateral limbs, trunk, or face. Evoked movements of the limb were generally maximal about a single joint. 3. There was a differential response to microstimulation between subnuclei of the motor thalamus. In order of decreasing frequency, the percentages of sites within each subnucleus from which movements were evoked were as follows: VPLo, 93% (449 of 483); VLo, 21% (57 of 272); VLc, 11% (15 of 140); VA, 1% (1 of 85); and reticular nucleus, 0% (0 of 65). In VPLc, 44% (34 of 78) of sites examined were microexcitable. However, these were almost all within 500 microns of the border of VPLo, suggesting they may have occurred as a result of current spread to adjacent VPLo. Although area X was not sampled in its entirety, it did not appear to be microexcitable. 4. Microexcitable responses had a somatotopic organization, similar to that for neuronal responses to sensorimotor examination, with leg responses found most laterally and arm and face responses found progressively more medially. 5. Zones in VPLo generally ranging from 500 to 1,500 microns were found in which microstimulation resulted in the same motor response. These microexcitable zones resemble those described for the striatum and were termed thalamic microexcitable zones (TMZ). TMZs also resemble cortical efferent zones in that both are somatotopically organized, may affect a single muscle or group of muscles, have low thresholds for microstimulation with sharp boundaries that lie adjacent to other microexcitable zones with the opposite effects, and are of approximately the same dimension. 6. This study suggest that a fundamental unit of motor organization, i.e., single muscle or joint, is preserved at the thalamic level in the form of TMZs, and that these fundamental units of organization may contribute to the modular organization of the cortex.

On the relations between single cell activity in the motor cortex and the direction and magnitude of three-dimensional static isometric force

We examined the relations between the steady-state frequency of discharge of cells in the arm area of the motor cortex of the monkey and the direction and magnitude of the three-dimensional static force exerted by the arm on an isometric manipulandum. Data were analyzed from two monkeys (n = 188 cells) using stepwise multiple linear regression. In 154 of 188 (81.9%) cells the regression model was statistically significant (P < 0.05). In 121 of 154 (78.6%) cells the direction but not the magnitude of force had a statistically significant effect on cell activity; in 11 of 154 (7.1%) cells only the magnitude effect was significant; and in 22 of 154 (14.3%) cells both the direction and magnitude effects were significant. The same analysis was used to assess the effect of the direction and magnitude of force on the electromyographic activity of 9 muscles of the arm and shoulder girdle. The regression model was statistically significant. For all the muscles studied in 4 of 9 (44.4%) muscles only the direction effect was significant whereas in the remaining 5 of 9 (55.6%) muscles both the direction and the magnitude were significant. No muscle studied showed a significant effect of force magnitude alone. These differences in the frequency of occurrence of directional and magnitude effects between cells and muscles were statistically significant (P < 0.005, chi 2 test). These findings underscore the fundamental importance of the direction of force in space for both motor cortical cells and proximal muscles and underline the differential relations of the cells and muscles to the direction and magnitude of force. These results indicate that the specification of the magnitude of three-dimensional force is embedded within the directional signal; this combined direction+magnitude effect was 3.9 times more prevalent in the muscles than in the cells studied. In contrast, the pure directional effect was 1.8 times more prevalent in the cells than in the muscles studied. This suggests that the direction of force can be controlled independently of its magnitude and that this direction signal is especially prominent in the motor cortex.

Functional imaging of the motor system

Recent studies of the motor system using functional imaging have served to emphasize the complexity of the control of even relatively simple movements. The results of these studies suggest that the behavioral context of the movement is an important determinant of functional activation within cortical motor areas.

Movement parameters and neural activity in motor cortex and area 5

The relations of ongoing single-cell activity in the arm area of the motor cortex and area 5 to parameters of evolving arm movements in two-dimensional (2D) space were investigated. A multiple linear regression model was used in which the ongoing impulse activity of cells at time t + tau was expressed as a function of the (X, Y) components of the target direction and of position, velocity, and acceleration of the hand at time t, where tau was a time shift (-200 to +200 msec). Analysis was done on 290 cells in the motor cortex and 207 cells in area 5. The time shift at which the highest coefficient of determination (R2) was observed was determined and the statistical significance of the model tested. The median R2 was 0.581 and 0.530 for motor cortex and area 5, respectively. The median shift at which the highest R2 was observed was -90 and +30 msec for motor cortex and area 5, respectively. For most cells statistically significant relations were observed to all four parameters tested; most prominent were the relations to target direction and least prominent those to acceleration.

Physiologic properties and somatotopic organization of the primate motor thalamus

1. To examine the functional organization of the primate "motor" thalamus, neuronal activity was studied systematically in awake behaving monkeys throughout the nucleus ventralis lateralis, pars oralis (VLo), nucleus ventralis posterior lateralis, pars oralis (VPLo), ventralis lateralis, pars caudalis (VLc), and portions of ventralis anterior (VA) and Area X. In addition, portions of the sensory nucleus ventralis posterior lateralis, pars caudalis (VPLc) were explored. Isolated neurons were examined for their responses to somatosensory examination and active movement (n = 919) and for their response to torque-induced joint displacements (n = 375). A total of 684 neurons was determined histologically to lie within specific subnuclei of the motor (n = 574) or sensory (n = 110) thalamus. 2. The sensorimotor response properties of neurons in the thalamic subnuclei showed clear differences in their response to somatosensory examination. In order of decreasing frequency, the percent of neurons responding to passive somatosensory examination in each subnucleus were as follows: VPLc, 96% (106/110), VPLo, 93% (252/270), VLc, 77% (43/56), VLo, 37% (59/155), Area X, 22% (12/53), and VA, 12% (5/40). Conversely, neurons that responded only to active movement were most frequent in VLo, 44% (68/155), VA, 45% (18/40), and Area X, 40% (21/53) and relatively infrequent in VLc 11% (6/56) and VPLo, 3% (7/270). In VPLc, no neurons were found that responded only to active movement (0/110). 3. A well-defined somatotopic organization was found in VLo, VPLo, and VPLc and was suggested strongly for VLc. Individual body regions were represented in a series of lamellae, organized in a partial onion skin-like arrangement with the leg represented in the outermost lamella, and the trunk, arm, and orofacial regions represented in successively deeper lamellae. In general the body representations, although present for each subnucleus thoroughly examined, i.e., VLo, VPLo, and VPLc, also were contiguous across subnuclei. Based on the available data, a clear somatotopic picture could not be discerned for Area X or VA. 4. Responses to torque application were more common in neurons in VPLo (77%; 60/78) and VLc (73%; 16/22) than in VLo (44%; 12/27). Mean latencies were shortest for neurons in VPLo (25 +/- 14 ms; mean +/- SD) and the bordering (shell) region of VPLc (22 +/- 15 ms) and were approximately twice as long in VLc (51 +/- 23 ms) and VLo (47 +/- 21 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Functional magnetic resonance imaging of motor cortex: hemispheric asymmetry and handedness

A hemispheric asymmetry in the functional activation of the human motor cortex during contralateral (C) and ipsilateral (I) finger movements, especially in right-handed subjects, was documented with nuclear magnetic resonance imaging at high field strength (4 tesla). Whereas the right motor cortex was activated mostly during contralateral finger movements in both right-handed (C/I mean area of activation = 36.8) and left-handed (C/I = 29.9) subjects, the left motor cortex was activated substantially during ipsilateral movements in left-handed subjects (C/I = 5.4) and even more so in right-handed subjects (C/I = 1.3).

Motor cortical activity preceding a memorized movement trajectory with an orthogonal bend

Two monkeys were trained to make an arm movement with an orthogonal bend, first up and then to the left ([symbol: see text]), following a waiting period. They held a two-dimensional manipulandum over a spot of light at the center of a planar working surface. When this light went off, the animals were required to hold the manipulandum there for 600-700 ms and then move the handle up and to the left to receive a liquid reward. There were no external signals concerning the "go" time or the trajectory of the movement. It was hypothesized that during that period signs of directional processing relating to the upcoming movement would be identified in the motor cortex. Following 20 trials of the memorized movement trajectory, 40 trials of visually triggered movements in radially arranged directions were performed. The activity of 137 single cells in the motor cortex was recorded extracellularly during performance of the task. It was found that 62.8% of the cells changed activity during the memorized waiting period. During the waiting period, the population vector (Georgopoulos et al. 1983, 1984) began to grow approximately 130 ms after the center light was turned off; it pointed first in the direction of the second part of the memorized movement (<--) and then rotated clockwise towards the direction of the initial part of the movement (increases). These findings indicate processing of directional information during the waiting period preceding the memorized movement. This conclusion was supported by the results of experiments in ten human subjects, who performed the same memorized movement ([symbol: see text]). In 10% of the trials a visual stimulus was shown in radially arranged directions in which the subjects had to move; this stimulus was shown at 0, 200, and 400 ms from the time the center light was turned off. We found that as the interval increased the reaction time shortened for the visual stimulus that was in the same direction as the upward component of the memorized movement.

Functional imaging of human motor cortex at high magnetic field

1. We used conventional gradient echo magnetic resonance imaging (MRI) at high field strength (4 Tesla) to functionally image the right motor cortex in six normal human subjects during the performance of a sequence of self-paced thumb to digit oppositions with the left hand (contralateral task), the right hand (ipsilateral task), and both hands (bilateral task). 2. A localized increase in activity in the lateral motor cortex was observed in all subjects during the task. The area of activation was similar in the contralateral and bilateral tasks but 20 times smaller in the ipsilateral task. The intensity of activation was 2.3 times greater in the contralateral than the ipsilateral task.

Motor cortical activity in a memorized delay task

Two rhesus monkeys were trained to move a handle on a two-dimensional (2D) working surface in directions specified by a light at the plane. They first captured with the handle a light on the center of the plane and then moved the handle in the direction indicated by a peripheral light (cue signal). The signal to move (go signal) was given by turning off the center light. The following tasks were used: (a) In the non-delay task the peripheral light was turned on at the same time as the center light went off. (b) In the memorized delay task the peripheral light stayed on for 300 ms and the center light was turned off 450-750 ms later. Finally, (c) in the non-memorized delay task the peripheral light stayed on continuously whereas the center light went off 750-1050 ms after the peripheral light came on. Recordings in the arm area of the motor cortex (N = 171 cells) showed changes in single cell activity in all tasks. In both delay tasks, the neuronal population vector calculated every 20 ms after the onset of the peripheral light pointed in the direction of the upcoming movement, which was instructed by the cue light. Moreover, the strength of the population signal showed an initial peak shortly after the cue onset in both the memorized and non-memorized delay tasks but it maintained a higher level during the memorized delay period, as compared to the non-memorized task.(ABSTRACT TRUNCATED AT 250 WORDS)

The motor cortex and the coding of force

The relation of cellular activity in the motor cortex to the direction of two-dimensional isometric force was investigated under dynamic conditions in monkeys. A task was designed so that three force variables were dissociated: the force exerted by the subject, the net force, and the change in force. Recordings of neuronal activity in the motor cortex revealed that the activity of single cells was directionally tuned and that this tuning was invariant across different directions of a bias force. Cell activity was not related to the direction of force exerted by the subject, which changed drastically as the bias force changed. In contrast, the direction of net force, the direction of force change, and the visually instructed direction all remained quite invariant and congruent and could be the directional variables, alone or in combination, to which cell activity might relate.

Amyloid myopathy presenting with respiratory failure

Amyloidosis is a rare cause of myopathy. Its prominent or presenting feature may be respiratory failure. Physiological measurement of transdiaphragmatic pressure and biopsy specimens of muscle show the pathological mechanism to be diaphragm weakness due to amyloid infiltration of the diaphragm rather than parenchymal lung involvement. Thus amyloid myopathy even without the typical macroglossia and muscle pseudohypertrophy should be considered as one of the neurological causes of respiratory failure.

Cortical control of motor behavior at the cellular level

The studies reviewed in this paper describe the relations of single-cell activity in central motor structures to complex visuomotor tasks and document the fact that various cortical areas process visuomotor information in parallel. Moreover, the studies provide clear evidence that the map in the motor cortex is modifiable and dynamically maintained.

Microsaccadic flutter

Microsaccadic flutter is a rare symptomatic saccadic oscillation that has been reported only twice previously. Here we describe 5 patients with this disorder. The oscillation is horizontal, has a frequency of 15-30 Hz, an amplitude of 0.1-0.5 degrees, and cannot be seen with the unaided eye. It is usually not associated with any underlying neurological disorder. We hypothesize that microsaccadic flutter is due to malfunction of the brainstem omnipause neurons.

Acquired pendular nystagmus in toluene addiction

We studied the ocular motor abnormalities in 4 patients chronically addicted to sniffing glue containing toluene. They showed acquired pendular nystagmus with horizontal and vertical components. One patient also showed saccadic oscillations. The pendular nystagmus may be a manifestation of a disturbance in brainstem-cerebellar connections secondary to the toxic effect of toluene on white matter.

Esophageal function in diabetes mellitus with special reference to acid studies and relationship to peripheral neuropathy

Esophageal function in 20 subjects with diabetes mellitus was assessed using esophageal manometry, 24-hr ambulatory esophageal pH monitoring, and esophageal scintigraphy. Seven patients had abnormal esophageal manometric studies, and this abnormality was significantly associated with peripheral neuropathy. Almost half of the subjects studied demonstrated excessive gastroesophageal acid reflux, but there was no correlation between the likelihood of abnormal reflux and the presence of peripheral neuropathy. Esophageal scintigraphy was relatively insensitive in the detection of abnormal esophageal function in diabetics.