Cortical control of visually guided reaching: evidence from patients with optic ataxia

The dorsal stream of visual information processing connecting V1 to the parietal cortex is thought to provide a fast control of visually guided reaching. Important for this assumption was the observation that in both the monkey and the human, parietal lesions may provoke disturbance of visually goal-directed hand movements. In the human, severe misreaching termed 'optic ataxia' has been ascribed to lesions of the superior parietal lobule (SPL) and/or the intraparietal sulcus. Using new tools for lesion analysis, here we re-evaluated this view investigating the typical lesion location in a large group of unilateral stroke patients with optic ataxia, collected over a time period of 15 years. We found no evidence for the assumption that disruption of visually guided reaching in humans is associated with a lesion typically centering on the SPL on the convexity. In both left and right hemispheres, we found optic ataxia associated with a lesion overlap that affected the lateral cortical convexity at the occipito-parietal junction, i.e. the junction between the inferior parietal lobule (IPL) and superior occipital cortex and--in the left hemisphere even more posteriorly--also the junction between occipital cortex and the SPL. Via the underlying parietal white matter, the lesion overlap extended in both hemispheres to the medial cortical aspect, where it affected the precuneus close to the occipito-parietal junction. These lateral and medial structures seem to be integral to the fast control of visually guided reaching in humans.     

Decoding the cortical transformations for visually guided reaching in 3D space

To explore the possible cortical mechanisms underlying the 3-dimensional (3D) visuomotor transformation for reaching, we trained a 4-layer feed-forward artificial neural network to compute a reach vector (output) from the visual positions of both the hand and target viewed from different eye and head orientations (inputs). The emergent properties of the intermediate layers reflected several known neurophysiological findings, for example, gain field-like modulations and position-dependent shifting of receptive fields (RFs). We performed a reference frame analysis for each individual network unit, simulating standard electrophysiological experiments, that is, RF mapping (unit input), motor field mapping, and microstimulation effects (unit outputs). At the level of individual units (in both intermediate layers), the 3 different electrophysiological approaches identified different reference frames, demonstrating that these techniques reveal different neuronal properties and suggesting that a comparison across these techniques is required to understand the neural code of physiological networks. This analysis showed fixed input-output relationships within each layer and, more importantly, within each unit. These local reference frame transformation modules provide the basic elements for the global transformation; their parallel contributions are combined in a gain field-like fashion at the population level to implement both the linear and nonlinear elements of the 3D visuomotor transformation.     

Contributions of the motor cortex to adaptive control of reaching depend on the perturbation schedule

During adaptation, motor commands tend to repeat as performance plateaus. It has been hypothesized that this repetition produces plasticity in the motor cortex (M1). Here, we considered a force field reaching paradigm, varied the perturbation schedule to potentially alter the amount of repetition, and quantified the interaction between disruption of M1 using transcranial magnetic stimulation (TMS) and the schedule of perturbations. In the abrupt condition (introduction of the perturbation on a single trial followed by constant perturbation), motor output adapted rapidly and was then followed by significant repetition as performance plateaued. TMS of M1 had no effect on the rapid adaptation phase but reduced adaptation at the plateau. In the intermediate condition (introduction of the perturbation over 45 trials), disruption of M1 had no effect on the phase in which motor output changed but again impaired adaptation when performance had plateaued. Finally, when the perturbation was imposed gradually (over 240 trials), the motor commands continuously changed during adaptation and never repeated, and disruption of M1 had no effect on performance. Therefore, TMS of M1 appeared to reduce adaptation of motor commands during a specific phase of learning: when motor commands tended to repeat.     

Activation of the supplementary motor area (SMA) during performance of visually guided movements

The supplementary motor area (SMA) has long been thought to have a special role in the internal generation of complex movements. Yet, a number of recent functional imaging studies indicate that the SMA is activated during the execution of simple movements guided by sensory cues. The extent of participation of the cingulate motor areas in visually guided movements also is unclear. To explore these issues we used the 2-deoxyglucose (2DG) technique to measure functional activation in the motor areas on the medial wall of the hemisphere in monkeys trained to perform visually guided reaching movements to randomly presented targets. This approach enabled us to make precise comparisons between sites of activation and the location of specific premotor areas on the medial wall of the hemisphere. We found that the SMA was strongly activated during reaching to different visual targets. Indeed, its activation was comparable to that of the primary motor cortex (M1). In contrast, none of the cingulate motor areas displayed significantly increased activation specifically related to arm movements. Our results provide further support for the involvement of the SMA in visually guided movements. Furthermore, our observations suggest that during externally guided reaching, SMA activation is tightly coupled to that of M1, but dissociated from that of the cingulate motor areas.     

Temporal relation of population activity in visual areas MT/MST and in primary motor cortex during visually guided tracking movements

There is growing evidence that in primate cerebral cortex the areas along the 'dorsal pathway' are involved in the transformation of visual motion information towards a motor command. To pursue this cortical flow of information from visual motion areas to the motor cortex, single-cell activity was recorded from visual areas MT/MST (middle temporal area/medial superior temporal area) and from primary motor cortex (M1) while monkeys tracked moving targets with their right hand. Spike activity of 353 directionally tuned motor cortex cells was combined to a time-varying population vector, and similarly a time-resolved visual population vector was calculated from 252 MT/MST cells. Both population vectors code faithfully for the direction of the collinear motion of target and hand. For a given direction, the length of the population vectors varied over time during the performance of the task. The temporal evolution of both population responses reflects the different relationship between the early visual responses to the moving target and the directional motor command controlling the hand movement. The results indicate that during the visual tracking task visual and motor populations which code for similar directions of movement are co-activated with considerable temporal overlap. Despite this co-activation in both modalities, we failed to observe any significant synchronization between areas MT/MST and M1.     

Contributions of alimentary tract surgery to modern infection control

The continuing contributions of alimentary tract operations to a clarification of the clinical utility of devices, procedures, and medications for control of surgical wound infection have been crucial to the advancement of modern surgical practice. Indeed, the foregoing essay has outlined several areas in which additional analysis and clarification should be able to further define valuable methods and combinations thereof. It has been the willingness of the individual surgeon oriented to the alimentary tract to include his operations and his patients in these kinds of rigid trials that have, indeed, allowed a final emergence of these useful adjuncts to the surgical armamentarium, an effect that now pervades all surgical practice.     

Trajectories of target reaching arm movements in individuals with spinal cord injury: effect of external trunk support

DESIGN: Deficits in trunk control due to spinal cord injury (SCI) lead to slower target-reaching movements of the hand. We investigated whether the movement path is also affected, and whether providing external support for the trunk can abolish the kinematic differences. OBJECTIVE: To compare movement trajectories between individuals with SCI and neurologically normal individuals, with and without external trunk support. SETTING: Neural Control/Biomechanics Laboratory, University of Illinois, Chicago, USA. METHODS: Five subjects with levels of injury between C7 and T4 were tested 3-8 years post-injury, and compared with five control subjects. Two targets were employed. Trajectories were recorded by a motion-capture system using infrared emitting markers. Peak speed and path curvature were calculated for the fingertip and for the acromion. RESULTS: Compared with control subjects, the subjects with SCI exhibited lower peak speed of the fingertip but not of the acromion, and less straight paths for both. When the trunk was supported externally, the difference in fingertip speed persisted. The support abolished the difference in path curvature for the fingertip but accentuated that for the acromion. CONCLUSION: The slower hand movements of individuals with SCI are not simply time-scaled versions of those of normal subjects, and the provision of trunk support does not erase the kinematic differences between the reaching movements of the two groups.     

One-year clinical course following visually guided irrigation for chronic closed lock of the temporomandibular joint.

OBJECTIVE: This study aimed to explore the clinical course following visually guided irrigation (VGIR) for chronic closed lock (CCL) of the temporomandibular joint (TMJ) as well as the factors of importance for clinical outcome. Evaluation emphasis was placed on the period needed for the patients to reach the success criteria. STUDY DESIGN: Sixty-one patients with unilateral CCL comprised the study group. The cumulative success rate of VGIR and the additional surgical treatments following VGIR were studied. The 61 patients were divided into either the good outcome (g) group or poor outcome (p) group on the basis of whether they reached the success criteria within 3 months postoperatively, and clinical and arthroscopic factors were correlated with the clinical outcome of VGIR. RESULTS: The cumulative success rate of VGIR increased up to the 6-month follow-up (success rate of 72.1%) but did not change after that point in time. A repeated VGIR (success rate of 87.5%) was performed in 8 patients. Open TMJ surgery (success rate of 87.5%) was performed in 8 patients, 7 of whom had an interfering condylar osteophyte. A pronounced reduction of preoperative painless range of mandibular motion (P-ROM) and advanced osteoarthritis (OA) were more frequently found in the p-group than in the g-group. The multivariate adjusted odds ratio showed that a decreased preoperative P-ROM was significantly predictive for a poor outcome of VGIR. CONCLUSIONS: The efficacy of VGIR is clinically acceptable as an initial surgical treatment for TMJ CCL. A 6-month follow-up period ought to be sufficient for outcome assessment of VGIR. A pronounced reduction of preoperative P-ROM should be considered as a risk factor for delay of the postoperative improvement, and OA changes may sometimes affect the clinical outcome of VGIR.     

Cytokine and clinical predictors for treatment outcome of visually guided temporomandibular joint irrigation in patients with chronic closed lock.

PURPOSE: This study investigates selected predictors for clinical outcome of temporomandibular joint (TMJ) irrigation in patients with chronic closed lock (CCL). PATIENTS AND METHODS: Fifty-six patients with unilateral CCL, who underwent a visually guided TMJ irrigation (VGIR), were enrolled in this study. They were divided into either successful (s-group; n = 38) or unsuccessful groups (u-group; n = 18), according to the clinical success criteria. The investigated predictive factors were age, gender, duration of symptoms before the VGIR, preoperative painless range of mandibular motion, preoperative self-evaluated TMJ pain on visual analog scale (VAS), severity of arthroscopically observed pathologies, and presence and concentrations of a set of pro- and anti-inflammatory cytokines (ie, tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, IL-6, IL-8, IL-12, and IL-10) in the aspirated synovial fluid (A-SF). Several comparative analyses and logistic regression analyses were used for statistical studies. RESULTS: The preoperative VAS score, detection rate of IL-8, and concentrations of IL-6 and IL-8 in the A-SF were significantly higher in the u-group (P < .05). Conversely, the detection rate and concentrations of IL-10 were significantly higher in the s-group (P < .05). The multivariate adjusted odds ratio (OR) showed that the detectable IL-10 in the A-SF (OR, 10.882; P = .047) is significantly predictive for a successful VGIR. CONCLUSIONS: The presence of IL-10 in the A-SF is a significant predictor of successful outcome of TMJ irrigation for CCL. Severe TMJ pain and detectable IL-6 or IL-8 in the A-SF seem to indicate a poor outcome after TMJ irrigation.     

Distribution of activity across the monkey cerebral cortical surface, thalamus and midbrain during rapid, visually guided saccades

To examine the distribution of visual and oculomotor activity across the macaque brain, we performed functional magnetic resonance imaging (fMRI) on awake, behaving monkeys trained to perform visually guided saccades. Two subjects alternated between periods of making saccades and central fixations while blood oxygen level dependent (BOLD) images were collected [3 T, (1.5 mm)3 spatial resolution]. BOLD activations from each of four cerebral hemispheres were projected onto the subjects' cortical surfaces and aligned to a surface-based atlas for comparison across hemispheres and subjects. This surface-based analysis revealed patterns of visuo-oculomotor activity across much of the cerebral cortex, including activations in the posterior parietal cortex, superior temporal cortex and frontal lobe. For each cortical domain, we show the anatomical position and extent of visuo-oculomotor activity, including evidence that the dorsolateral frontal activation, which includes the frontal eye field (on the anterior bank of the arcuate sulcus), extends anteriorly into posterior principal sulcus (area 46) and posteriorly into part of dorsal premotor cortex (area 6). Our results also suggest that subcortical BOLD activity in the pulvinar thalamus may be lateralized during voluntary eye movements. These findings provide new neuroanatomical information as to the complex neural substrates that underlie even simple goal-directed behaviors.     

Contributions to the management of intraabdominal infections

Intraabdominal infection represents a spectrum of diseases with a common pathogenesis. Establishing a prompt diagnosis and avoiding treatment delays are keys to achieving the best outcomes. Mortality depends on initiating early appropriate treatment to restore fluid and electrolyte imbalances, supporting the function of vital organs, providing appropriate broad-spectrum antimicrobial therapy, and achieving adequate source control. Faculty from the Department of Surgery at the University of Louisville have made significant contributions to the understanding and management of intraabdominal infections that have affected clinical practice and patient outcomes.     

Contributions to the mechanism of action of beta-adrenergic stimulants

Subcellar localization of ionic Ca was investigated by the Pb-acetate cytochemical method in rat myometrium on the 21st day of pregnancy, following oxytocin and Bricanyl treatment. Following Oxytocin treatment the amount of ionic Ca increased in the muscle cells of the uterus and decreased in the plasma membrane and mitochondria as compared with the control. Tocolytics given in the last four days of pregnancy caused a decrease in the cytoplasmic concentration of ionic Ca and increased the Ca++ content of Ca++ pools (plasma membrane, mitochondrium). The change in the intracellular distribution of Ca++ may be involved in the mechanism of action of tocolytics and in the development of the relaxation of smooth muscle.