Eye position representation in human anterior parietal cortex

Eye position helps locate visual targets relative to one's own body and modulates the distribution of attention in visual space. Whereas in the monkey, proprioceptive eye position signals have been recorded in the somatosensory cortex, in humans, no brain site has yet been associated with eye position. We aimed to disrupt the proprioceptive representation of the right eye in the left somatosensory cortex, presumably located near the representation of the right hand, using repetitive transcranial magnetic stimulation (rTMS). Head-fixed subjects reported their perceived visual straight-ahead position using both left and right eye monocular vision, before and after 15 min of 1 Hz rTMS. rTMS over left somatosensory but not over left motor cortex shifted the perceived visual straight ahead to the left, whereas nonvisual detection of body midline was unchanged for either brain area. These results can be explained by the underestimation of the angle of gaze of the right eye when fixating the target. To link this effect more tightly to an altered ocular proprioception, we applied a passive deviation to the right eye before the visual straight-ahead task. Passive eye displacement modulated the shift in the perceived straight ahead induced by somatosensory rTMS, without affecting the perceived straight ahead at baseline or after motor cortex rTMS. We conclude that the anterior parietal cortex in humans encodes eye position and that this signal has a proprioceptive component

Evaluation of cervical proprioceptive function: optimizing protocols and comparison between tests in normal subjects

STUDY DESIGN: A test-retest design evaluated stability as well as within and between day reliability. \ud \ud OBJECTIVE: The study aimed to define optimum protocols for the cervical joint position error (JPE) and cervicocephalic kinesthesia tests and to investigate association between performances in the tests. \ud \ud SUMMARY OF BACKGROUND DATA: The cervical JPE and cervicocephalic kinesthesia tests are proposed as measures of cervical proprioception. However, there has been little investigation of the number of trials needed to obtain stable and reliable estimates of performance. Both tests have potential limitations in reflecting the underlying construct of cervical proprioception and association between performances in both has not been investigated previously. \ud \ud METHODS: Head repositioning and head-tracking errors were measured using an electromagnetic-tracking system in 16 normal subjects, tested on 3 occasions over 2 days. The effect of different numbers of trial repeats was analyzed descriptively in terms of stability of measures obtained and by using intraclass correlation coefficients to assess reliability. Association between the tests was analyzed with the Pearson correlation coefficient. \ud \ud RESULTS: Stable estimates of performance were obtained when data from 6 or more trials was included. The greatest test-retest reliability was obtained with 5 or more trials in both the cervical JPE (intraclass correlation coefficients = 0.73-0.84) and cervicocephalic kinesthesia (intraclass correlation coefficients = 0.90-0.97) tests. Correlation analyses indicated no significant association between performances in the 2 tests (r = -0.476-0.228, P > 0.05). \ud \ud CONCLUSION: Our finding that at least 6 trials were needed to optimize stability, and reliability of outcome measures has important implications for application of these tests. The lack of correlation between performances in the tests supports the suggestion that they are not comparable measures of cervical proprioception. Further planned studies will include a range of tests challenging different aspects of cervical proprioceptive contribution to sensorimotor control in different subcategories of neck pain patients

Multisensory integration in dynamical behaviors: maximum likelihood estimation across bimanual skill learning

Optimal integration of different sensory modalities weights each modality as a function of its degree of certainty (maximum likelihood). Humans rely on near-optimal integration in decision-making tasks (involving e.g., auditory, visual, and/or tactile afferents), and some support for these processes has also been provided for discrete sensorimotor tasks. Here, we tested optimal integration during the continuous execution of a motor task, using a cyclical bimanual coordination pattern in which feedback was provided by means of proprioception and augmented visual feedback (AVF, the position of both wrists being displayed as the orthogonal coordinates of a single cursor). Assuming maximum likelihood integration, the following predictions were addressed: (1) the coordination variability with both AVF and proprioception available is smaller than with only one of the two modalities, and should reach an optimal level; (2) if the AVF is artificially corrupted by noise, variability should increase but saturate toward the level without AVF; (3) if the AVF is imperceptibly phase shifted, the stabilized pattern should be partly adapted to compensate for this phase shift, whereby the amount of compensation reflects the weight assigned to AVF in the computation of the integrated signal. Whereas performance variability gradually decreased over 5 d of practice, we showed that these model-based predictions were already observed on the first day. This suggests not only that the performer integrated proprioceptive feedback and AVF online during task execution by tending to optimize the signal statistics, but also that this occurred before reaching an asymptotic performance level

Conflict Prevention in Estonia: The Role of the Electoral System

Estonia's success in averting a potential conflict over its Russian-speaking minority is often attributed to the intervention of the OSCE High Commissioner on National Minorities. Indeed, the Estonian case is one of the most satisfactory encounters in the period of Max van der Stoel's impressive diplomatic engagement. However, deeper, structural factors were also important over the longer term. In particular, the voting system that Estonia adopted, based on the single transferable vote system of proportional representation, turned out to be important in encouraging political moderation. This article argues that a decisive factor in ethnic accommodation was the way the political system channelled the activities of the Russian-speaking groups into Estonian parties. Other contributory factors were the weakness of ethnic identity among the Russian-speakers and international constraints on Russian foreign policy. This analysis highlights the crucial role of domestic institutions in conflict prevention

The cerebellum and motor dysfunction in neuropsychiatric disorders

The cerebellum is densely interconnected with sensory-motor areas of the cerebral cortex, and in man, the great expansion of the association areas of cerebral cortex is also paralleled by an expansion of the lateral cerebellar hemispheres. It is therefore likely that these circuits contribute to non-motor cognitive functions, but this is still a controversial issue. One approach is to examine evidence from neuropsychiatric disorders of cerebellar involvement. In this review, we narrow this search to test whether there is evidence of motor dysfunction associated with neuropsychiatric disorders consistent with disruption of cerebellar motor function. While we do find such evidence, especially in autism, schizophrenia and dyslexia, we caution that the restricted set of motor symptoms does not suggest global cerebellar dysfunction. Moreover, these symptoms may also reflect involvement of other, extra-cerebellar circuits and detailed examination of specific sub groups of individuals within each disorder may help to relate such motor symptoms to cerebellar morphology

State Estimation in the Cerebellum

An exciting hypothesis about the cerebellum is that its role is one of state estimation—a process that combines afferent copies of motor commands with afferent sensory signals to produce a representation of the current status of the peripheral motor system. Sensory inputs alone cannot provide a perfect state signal because of inevitable delays in their afferent pathways. We have recently reported the effects of transcranial magnetic stimulation (TMS) over the ipsilateral cerebellum as healthy subjects made rapid reaching movements towards visually defined targets (Miall et al. in PLoS Biology 5:2733–2744, 2007). Errors in the initial direction and in the final finger position of this reachto-target movement were consistent with the reaching movements being planned and initiated from an estimated hand position that was about 138 ms out of date. This interval is consistent with estimates of the delays in sensory motor pathways that would inform the central nervous system of the peripheral status. We now report new data using the same paradigm, testing the effects of varying the TMS stimulus train from one, two, or three pulses. We show that the errors in movement are relatively insensitive to the TMS pulse-train duration. The estimated time interval by which the hand position is mislocalized varied by only 12 ms as the TMS train duration increased by 100 ms. Thus, this interval is likely to reflect physiological processes within the cerebellum rather than the TMSstimulus duration. This new evidence supports our earlier claim that the cerebellum is responsible for predictively updating a central state estimate over an interval of about 120–140 ms. Dysfunction of the cerebellum, whether through disease or experimental procedures, leads to motor errors consistent with a loss of knowledge of the true state of the motor system

Functional imaging: is the resting brain resting?

It is often assumed that the human brain only becomes active to support overt behaviour. A new study challenges this concept by showing that multiple neural circuits are engaged even at rest. We highlight two complementary hypotheses which seek to explain the function of this resting activity

Drawing cartoon faces - a functional imaging study of the cognitive neuroscience of drawing

We report a functional imaging study of drawing cartoon faces. Normal, untrained participants were scanned while viewing simple black and white cartoon line-drawings of human faces, retaining them for a short memory interval, and then drawing them without vision of their hand or the paper. Specific encoding and retention of information about the faces was tested for by contrasting these two stages (with display of cartoon faces) against the exploration and retention of random dot stimuli. Drawing was contrasted between conditions in which only memory of a previously viewed face was available versus a condition in which both memory and simultaneous viewing of the cartoon was possible, and versus drawing of a new, previously unseen, face. We show that the encoding of cartoon faces powerfully activates the face sensitive areas of the lateral occipital cortex and the fusiform gyrus, but there is no significant activation in these areas during the retention interval. Activity in both areas was also high when drawing the displayed cartoons. Drawing from memory activates areas in posterior parietal cortex and frontal areas. This activity is consistent with the encoding and retention of the spatial information about the face to be drawn as a visuo-motor action plan, either representing a series of targets for ocular fixation or as spatial targets for the drawing actio

Steady-State movement related potentials for brain–computer interfacing

An approach for brain-computer interfacing (BCI) by analysis of steady-state movement related potentials (ssMRPs) produced during rhythmic finger movements is proposed in this paper. The neurological background of ssMRPs is briefly reviewed. Averaged ssMRPs represent the development of a lateralized rhythmic potential, and the energy of the EEG signals at the finger tapping frequency can be used for single-trial ssMRP classification. The proposed ssMRP-based BCI approach is tested using the classic Fisher's linear discriminant classifier. Moreover, the influence of the current source density transform on the performance of BCI system is investigated. The averaged correct classification rates (CCRs) as well as averaged information transfer rates (ITRs) for different sliding time windows are reported. Reliable single-trial classification rates of 88%-100% accuracy are achievable at relatively high ITRs. Furthermore, we have been able to achieve CCRs of up to 93% in classification of the ssMRPs recorded during imagined rhythmic finger movements. The merit of this approach is in the application of rhythmic cues for BCI, the relatively simple recording setup, and straightforward computations that make the real-time implementations plausible