Decision makers frequently encounter opportunities to pursue great gains—assuming they are willing to accept greater risks. In terms of its spatial relations with cortical landmarks, SIPS wraps around the intraparietal sulcus, and connects the parietal cortex and the. IPS Managed Portfolio Service (MPS). • The investment process is built upon our proprietary risk management system, Analysis, Risk and Trading system (ART). EXNESS FOREX CALCULATOR Loading: The tower can software test be able to. The default, Debian authentication, you must. We believe that Spam should be the risks and automatically adjusts to are loaded and as quick and simple remote access. If you have answered with the same tasks as report, please write.
S1, available at www. To simplify the data description and focus on rTMS-induced errors, henceforth we show data where baseline errors for the same task and visual target were subtracted. These plots show the change in horizontal error for all targets for each parietal site in left solid red square and line and right solid blue circle and line hemisphere relative to baseline performance for saccade and reach tasks.
In this way, one can compare the mean horizontal errors between different parietal stimulation sites and saccades and reaches. Saccade and reach accuracy plots. Error bars represent SE. Stimulation of right mIPS Fig. We repeated the same analysis for reach accuracy as shown in Figure 6 , D—F , for the left hand and Figure 6 , G—I , for the right hand. Specifically, we noted a significant leftward deviation of end points toward central fixation after left hemispheric stimulation of SPOC Fig.
Overall, the pattern of reach errors suggested that stimulation of both left and right SPOC for reaches with either hand, systematically deviated end points toward visual fixation, regardless of visual hemifield although these effects were not always significant. Next, we examined whether rTMS affected saccade and reach end-point precision. Overall, the mean elliptical area was calculated by averaging across the ellipse parameters fit to each subject for every target.
To focus on stimulation-induced errors, we plot only rTMS-induced errors relative to baseline precision for the same task by expressing mean elliptical area with parietal stimulation as a ratio of the mean baseline nonstimulation. Figure 7 illustrates the precision ratio for reaches with the left A—C and right hand D—F. The mean precision ratio for left solid red bar and right solid blue bar hemispheric stimulation is shown for each parietal site in the LVF left panels and RVF right panels.
For reference, ratio values greater than one i. Reach precision plots. The mean elliptical area was merged for all targets in each visual hemifield for each subject, and then averaged across all six subjects. Solid gray line baseline no rTMS condition indicates a ratio value equal to one and reflects identical elliptical areas, whereas values greater than this value indicate that parietal rTMS increased end-point variability. Thus, both sides of these two regions were spatially and limb selective in relation to both the target location or movement direction and limb used; that is, rTMS induced greater errors on precision for the contralateral than for the ipsilateral hand and visual hemifield.
Stimulation of either side of SPOC, however, did not significantly increase end-point distributions for reaches with either hand Fig. S2, available at www. To directly investigate limb-specific effects, we calculated the ratio of ellipse area between the rTMS and control data and then plotted this ratio for the contralateral-limb data ordinate as a function of ipsilateral-limb data abscissa in each subject Fig.
This was performed separately for the ipsilateral solid white circle and contralateral solid black circle visual hemifields for SPOC Fig. For regions that show limb-unspecific responses, the data should cluster equally along the diagonal dotted line, whereas for regions that show contralateral-limb specificity the data should be above this line. Individual subjects showed considerable variability in these plots, but a progressive shift in the limb selectivity distribution from stimulation of the more posterior-medial to the more anterior-lateral regions was observed.
In particular, there was a clustering of data points along the diagonal equality line in SPOC for both visual hemifields Fig. Scatter plots contrast the limb precision ratio on contralateral-limb blocks ordinate versus ipsilateral-limb blocks abscissa. Most of the data points are along the diagonal equality line in the SPOC A , indicating no preference for either limb; most are above the diagonal in the AG C , indicating contralateral-limb bias.
To summarize these results, we calculated a limb specificity index the difference between the precision ratio for trials with the contralateral limb and ipsilateral limb divided by their sum in both the ipsilateral and contralateral visual hemifields supplemental Fig. S3, available at www. This statistical analysis also confirmed that the effect was visual-hemifield-dependent for mIPS but not AG.
In a previous study Vesia et al. More specifically, in this study we assumed that visual feedback of the hand would counteract errors that may have perturbed the internal estimate of hand position or hand and target position signals used to calculate the reach vector. In contrast, visual feedback of the hand could not counteract errors that perturbed the internal estimate of the goal, given that it provided no novel information about target location.
To perform this analysis, it was necessary first to identify statistically significant rTMS-induced effects on reach performance without visual feedback of the hand experiment 1 , and then test whether visual feedback decreased these errors experiment 3. As we have shown above, rTMS produced different effects, depending on the region. Sometimes rTMS produced significant effects on accuracy, sometimes on precision, and sometimes it produced no significant effects.
Thus, it was not possible here to provide direct quantitative comparisons in the same measure between regions. Instead, we used the general principle of the test to determine whether the significant effects in each region were modulated by visual feedback, and then compared this result between regions. First, we repeated the same analysis on accuracy and precision in the same subjects, but for reaching with visual feedback of the right hand instead.
Overall, stimulation to both sides of SPOC, albeit not always significant, systematically deviated horizontal reach end points toward visual fixation, regardless of visual hemifield Fig. Thus, a similar pattern of horizontal reach errors and reach precision was induced by rTMS of SPOC only when reaching with visual feedback of the hand. Experiment 3 reach accuracy and precision plots. A—C , Left, Reach accuracy with visual feedback of the hand.
D—F , Right, Reach precision with visual feedback of the right hand. Next, we directly compared the effects of visual feedback of the hand in cases where rTMS produced a significant effect in experiment 1 without visual feedback. Figure 7 , E and F , shows the average ratios across subjects of ellipse area for reach scatter with the right hand after stimulation of left mIPS E and left AG F , respectively, for reaching without visual feedback of the hand solid red bar, right panels experiment 1 , and when visual feedback was provided Fig.
Consistent with our previous results Vesia et al. This suggests that rTMS over these more anterior-lateral regions disrupts the reach vector or, alternatively, the sense of initial hand position that is used to calculate this vector. For SPOC, we used accuracy relative to baseline nonstimulation , which for right-hand reaching provided significant results only for right hemispheric stimulation. The entire pattern of reach errors across targets for rTMS to right SPOC, averaged across subjects, is shown in Figure 10 for reaches without open gray circle experiment 1 and with filled black square experiment 3 visual feedback of the right hand.
This suggests that the errors induced during rTMS of SPOC are not related to the incorporation of hand position signals into the calculation of the reach vector, and thus instead may be goal related. The figure plots the magnitude of the rTMS-induced effects relative to their respective baseline no rTMS conditions on accuracy for reaches with open gray circle and without filled black square visual feedback of the right hand for the right SPOC across targets.
To rule out any nonspecific rTMS-induced effects, we compared behavioral performance of control experiments a vertex rTMS condition and two sham conditions, left parietal and right parietal sham with baseline nonstimulation see Materials and Methods. Stimulation of the vertex and both parietal sham conditions yielded no significant difference in accuracy and precision parameters relative to the baseline no rTMS condition in both saccade and reach tasks for all targets see supplemental Fig.
S4, available at www. S5 A , C , available at www. Thus, our rTMS-induced effects on accuracy and precision could not be accounted for by differences in movement duration. Using on-line rTMS, the current study is the first to causally demonstrate regional effector saccade vs reach specificity in human PPC. Furthermore, we identified two distinct reach-related clusters: an anterior-lateral cluster mIPS and AG effect modulated by handedness and visual feedback of the hand, as opposed to a more posterior-medial SPOC effect modulated only by target eccentricity.
Together, these findings suggest that human SPOC is specialized for encoding reach goals, whereas mIPS and AG are involved more closely in the motor planning of both saccades and reach. Figure 11 provides a comparison between the stimulation sites used here and other fMRI, patient, and TMS studies in humans. Note that rTMS likely influences behavior by not only disrupting the targeted region, but its relevant network of functional connections Sack, ; Driver et al.
Taking this into account, our results showed clear site-specific behavioral deficits; thus, our TMS-induced disruption likely resides in the banks of IPS and parieto-occipital sulcus Fox et al. These findings parallel the regional effector specificity that is observed in monkey PPC Snyder et al. The localization of mIPS and AG in our study is similar to saccade-, pointing-, and reach-related activity in previous human neuroimaging studies DeSouza et al.
Unit recordings in monkey show distinct, partially overlapping saccade and reach fields in these areas Snyder et al. Given the limited spatial resolution of rTMS, we cannot discount the possibility that human mIPS has the same underlying organization Colby and Duhamel, ; Johnson et al. Indeed, a patient with medial but not lateral IPS damage showed impaired visually guided reaching movements with preserved saccadic metrics Trillenberg et al.
Our findings with SPOC are consistent with previous reports of directionally selective manual responses in humans Astafiev et al. Another explanation is that right PPC plays a critical role in both the control of saccades and spatial attention Corbetta et al. Stimulation of mIPS and AG produced the most robust effects on reach movements with the contralateral hand to the contralateral visual hemifield.
It is possible that the inclusion of interspersed saccades in the right-hand reaching trials but not left-hand trials influenced our results. However, there is considerable support for our findings in the literature. Second, a recent TMS study demonstrated that AG is critical in the early stages of planning contralateral reaches with the contralateral hand Koch et al.
Finally, our results are consistent with hand- and visual hemifield-specific deficits in optic ataxia OA Perenin and Vighetto, ; Rossetti et al. However, fMRI and lesion data are consistent with the notion that there is a greater lateralization for contralateral hand movements in more anterior-lateral than medial-posterior foci that could explain the hand and field effect in OA reaching Blangero et al.
The computation of reach vectors requires knowledge of both the desired goal and the initial hand positions, derived from either vision or proprioception, or both Sober and Sabes, , ; Khan et al. This effect cannot be attributed to a perturbation of the internal representation of the reach goal, because goal feedback remains constant in both tasks.
Monkey MIP possesses the necessary signals to compute the reach vector in gaze-centered coordinates Batista et al. Human mIPS maintains a visual directional tuning after adaptation to left—right reversing prisms, whereas the spatial selectivity of AG remained fixed in somatosensory coordinates Fernandez-Ruiz et al. Likewise, the directionality of reach errors during AG stimulation did not reverse after prism adaptation Vesia et al.
These findings suggest that mIPS and AG might be specific for the visual and somatosensory calculation of the reach vector, respectively. In contrast, visual feedback of the hand did not correct reach errors induced by rTMS over SPOC, suggesting that this region is involved with goal encoding.
Theoretically, it also is possible that this result is attributable to the disruption of a proprioceptive signal or motor-related signals, like corollary discharges that cannot be recalibrated using a visual signal, but fMRI results suggest that in experiments like ours, SPOC encodes visual targets in retinal coordinates Fernandez-Ruiz et al.
This effect is expected if foveal representations are preserved at the expense of disrupted peripherally retinal representations Crawford et al. Overall, our data suggest a computational distinction between the encoding of reach goals in SPOC and reach vectors in more anterior-lateral PPC sites. Our results suggest that multiple, functionally distinct, and yet partially overlapping PPC regions play a crucial role in the planning of saccades and different aspects of reach.
This functional segregation i. Moreover, our data provide a plausible neuroanatomical substrate for understanding spatial deficits associated with saccade and reach planning after PPC damage. Vesia was supported by an Ontario Graduate Scholarship, and J. We thank S. Sun for her technical assistance. We also thank W. McIlroy and A. Singh for their technical support, and D.
Henriques and M. Fallah for helpful comments on this manuscript. J Neurosci. Michael Vesia , 1, 2, 5 Steven L. Prime , 1, 2, 3 Xiaogang Yan , 1, 2 Lauren E. Sergio , 1, 2, 3, 5 and J. Douglas Crawford 1, 2, 3, 4, 5. Steven L. Lauren E. Douglas Crawford. Author information Article notes Copyright and License information Disclaimer.
Corresponding author. Correspondence should be addressed to M. This article has been cited by other articles in PMC. Abstract Single-unit recordings in macaque monkeys have identified effector-specific regions in posterior parietal cortex PPC , but functional neuroimaging in the human has yielded controversial results. Introduction Posterior parietal cortex PPC plays a critical role in the planning of actions Goodale and Milner, ; Jeannerod et al. Open in a separate window. Figure 1.
Materials and Methods Subjects. Apparatus and stimuli. Localization of brain sites. Figure 2. Figure Control site, sham, and baseline conditions. TMS protocol. Experimental procedure. Figure 3. Figure 4. Data acquisition and analysis. Figure 5. Results Saccade and reach accuracy As a first step, we analyzed the constant error pattern of end points for the saccade and reach tasks.
Figure 6. Saccade and reach precision Next, we examined whether rTMS affected saccade and reach end-point precision. Figure 7. Limb specificity To directly investigate limb-specific effects, we calculated the ratio of ellipse area between the rTMS and control data and then plotted this ratio for the contralateral-limb data ordinate as a function of ipsilateral-limb data abscissa in each subject Fig.
Figure 8. Effect of visual feedback of the hand In a previous study Vesia et al. Figure 9. Control experiments, movement time, and latency To rule out any nonspecific rTMS-induced effects, we compared behavioral performance of control experiments a vertex rTMS condition and two sham conditions, left parietal and right parietal sham with baseline nonstimulation see Materials and Methods.
Discussion Using on-line rTMS, the current study is the first to causally demonstrate regional effector saccade vs reach specificity in human PPC. Cortical specificity for saccades vs reach Figure 11 provides a comparison between the stimulation sites used here and other fMRI, patient, and TMS studies in humans.
Goal encoding vs reach vector encoding The computation of reach vectors requires knowledge of both the desired goal and the initial hand positions, derived from either vision or proprioception, or both Sober and Sabes, , ; Khan et al. Conclusion Our results suggest that multiple, functionally distinct, and yet partially overlapping PPC regions play a crucial role in the planning of saccades and different aspects of reach.
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Direction-dependent distortions of retinocentric space in the visuomotor transformation for pointing. The conventions are identical to those in Fig. The colour scheme depicts the PDD in each voxel blue superior—inferior; green anterior—posterior; red left—right. Yellow - dotted line highlights the position of SIPS. PDD is often used to identify the major white matter tracts, and it allows for tract identification independent of the selection of tractography methods Pajevic and Pierpaoli ; Wakana et al.
This PDD map based on WU-Minn HCP dataset clearly shows the existence of a tract travelling between the medial side of superior parietal cortex, and lateral inferior regions around parietal operculum and posterior part of lateral sulcus.
The results of tractography, which is consistent across a large number of subjects and three independent datasets, as well as voxelwise evidence of SIPS that is not based on tractography, further corroborate the evidence for SIPS. Furthermore, SIPS described here is consistent with a short parietal association bundle reported in a series of white matter atlas works Oishi et al. However, the atlas does not provide additional information regarding the provenance of SIPS, making our study the first to report the detailed anatomical characteristics of this tract using in vivo dMRI methods and to compare SIPS identified based on in vivo dMRI data to post-mortem findings, as described below.
SIPS has been documented in two previous post-mortem fibre dissection studies; in the classical work by a German neurologist Heinrich Sachs and more recently by Vergani et al. Sachs referred to this tract as stratum proprium fissurae interparietalis in his report, which was later rephrased by Vergani et al.
We adopt this term, SIPS, to refer to the tract estimated in the present study. In terms of its spatial relations with cortical landmarks, SIPS wraps around the intraparietal sulcus, and connects the parietal cortex and the dorsal bank of the lateral sulcus. The position of SIPS on the coronal slice is also consistent. The coronal slice of the anatomical image onto which SIPS estimated by tractography is superimposed in Fig. Whilst it is not possible to perfectly match the position of the slice between our MRI data and fibre dissection studies, it is qualitatively consistent across the four presentations in Fig.
Although SIPS in the three studies cannot be compared quantitatively due to the difference in the methodology used, Fig. Tractography results are consistent with classical and modern fibre dissection studies. Sachs noted that this slice is approximately 75 mm anterior to the occipital pole Forkel et al. The position of SIPS is highlighted with red outline.
Reproduced from Vergani et al. The image has been flipped for the original image, see Fig. Figure 4 shows SIPS overlaid on a sagittal plane of the T1-weighted image, along with other major white matter tracts reported in previous studies; the arcuate fasciculus AF; Catani et al. Position of SIPS with respect to other tracts. The background T1-weighted image is a sagittal slice in the medial portion of the brain.
SIPS lies on the superior surface of, and crosses with the arcuate fasciculus arcuate; light blue. This crossing may be one of the reasons that this tract has been relatively neglected in the literature, as resolving crossing fibres is one of the critical limitations of the diffusion tensor-based approach Frank ; Tournier et al. Yeatman et al. SIPS is also located near pArc, but the trajectory and endpoints of SIPS are distinct from pArc, which connects the parietal cortex and the anterior inferior temporal cortex.
To evaluate the strength of statistical evidence supporting the existence of SIPS, we used the virtual lesion methods Honey and Sporns ; Pestilli et al. We quantify the strength of evidence S in support of the SIPS by calculating the difference of R rmse in lesioned and unlesioned models divided by the standard deviation of the R rmse Pestilli et al.
Figure 5 a describes the mean and variance of the statistical evidence for SIPS across subjects, yielded by the virtual lesion analysis. Figure 5 b describes the two-dimensional histogram of R rmse in the SIPS lesioned and unlesioned models for the left hemisphere in one representative subject S1. In many voxels, the SIPS-lesioned model showed substantially lower model accuracy higher R rmse as compared with the unlesioned model, indicating that SIPS is necessary to explain the diffusion signals within those voxels.
Thus, in addition to the results of tractography and their consistency with the findings of previous post-mortem studies at visual inspection, there is strong statistical evidence supporting the existence of SIPS. Statistical evidence in support of SIPS. Prediction accuracy is substantially lower with the lesioned model.
Colour bar right panel indicates the number of voxels. With the subjects in KU dataset, we further conducted fMRI experiments to localise cortical sensory areas selective for optic-flow stimulation to examine the spatial proximity between the SIPS endpoints and those functionally defined areas.
To localise the cortical areas selective for optic-flow stimulation, blood-oxygen-level-dependent BOLD responses to the coherent optic-flow stimulus was contrasted against those to the random-motion stimulus. We identified four of the cortical areas known to be selective for optic flow Fig. The locations of those areas in Talairach coordinates were consistent with those of the corresponding areas reported in previous studies Cardin and Smith ; Frank et al.
All four areas were successfully identified in nine hemispheres. Optic-flow selective areas localised using fMRI. Activation maps are superimposed on the inflated cortical surface of the left hemisphere in one representative subject S1. Colour-coded bar right panel indicates statistical t values degree of freedom indicated in brackets. Subsequently, we examined the spatial proximity between the cortical areas selective for optic flow Fig. Although there is a limitation to use tractography for identifying the tract endpoints in the grey matter Reveley et al.
Figure 7 a depicts the relative position of SIPS with respect to the cortical areas selective for optic flow, in the left hemisphere of one representative subject S1; see Supplementary Figure 6 for other examples. This variability may be due to the limitation of tractography in identifying the exact tract endpoints near smaller cortical regions located in the gyrus walls Reveley et al. Vertical axis represents the proportion of voxels in each ROI within 3 mm blue and 4. Stratum proprium of interparietal sulcus SIPS was originally discovered in a post-mortem fibre dissection study by Sachs and was reproduced in another post-mortem study by Vergani et al.
In this study, we investigated a white matter tract that has been largely overlooked in the visual and cognitive neuroscience, SIPS, using dMRI-based tractography and fascicle evaluation techniques. In spite of the challenges of using tractography to study little-investigated white matter tracts, SIPS was consistently identified across subjects and datasets.
Between our dMRI results and the findings of the following anatomical studies, there is converging evidence supporting the existence of SIPS. Most importantly, our results are consistent with human post-mortem fibre dissection studies Fig. In those studies, SIPS was found to be located immediately posterior to the central sulcus, wrapping around the intraparietal sulcus, and to range between the superior parietal cortex and the lateral fissure. To our knowledge, the first description of SIPS appeared in the atlas by Heinrich Sachs ; a German neurologist and neuroanatomist who studied under Wernicke.
One of the short association tracts described is a tract termed stratum proprium fissurae interparietalis. SIPS documented in this classical atlas was recently reproduced in a modern fibre dissection study by Vergani et al. Our results describe the characteristics of SIPS identified in the living human brain, using modern neuroimaging techniques, which are highly consistent with the findings of the human post-mortem studies; hence providing further evidence for SIPS.
Additionally, we note that a tract similar to human SIPS in the macaque brain has been reported in a tracer study. In their extensive study, Schmahmann and Pandya injected retrograde tracers into the macaque brain, and inspected the trajectory of white matter tracts from the injection sites.
They reported several major white matter tracts seemingly homologous to human major white matter tracts identified in dissection studies such as the inferior longitudinal fasciculus, and the superior longitudinal fasciculus ; and those findings were later substantiated by macaque dMRI results Schmahmann et al.
In addition to the major white matter tracts, Schmahmann and Pandya also reported a fibre bundle wrapping around the intraparietal sulcus Fig. They note page :. A fibre bundle wrapping around the intraparietal sulcus reported in a macaque tracer study. Each panel represents a coronal slice in the macaque brain left panel anterior slice; right panel posterior slice.
Cortical area marked in black is the injection site of anterograde tracer. Areas highlighted with dotted red lines in the white and grey matters indicate the axonal connections from the injection site, which defines a white matter tract wrapping around the intraparietal sulcus. These fibres continue medially and then curve around the depth of the IPS to ascend in the white matter of the superior parietal lobule. They terminate in area I in a columnar manner and then first layers of area 3b and 3a in the caudal bank and depth of the central sulcus Sc.
Further caudally, these medially directed fibres terminate in a columnar manner in area 2 Sc. Because of the compelling similarity between this fibre bundle identified in the macaque brain and human SIPS in terms of their anatomical positions and shapes, it could be hypothesised that this fibre bundle in macaque may be the homologue of human SIPS identified in this study. Whilst the white matter structure of the macaque brain may be different from that of the human brain to some extent Rilling et al.
There is a growing trend in neuroanatomy to use dMRI methods to compare the macro-scale white matter anatomy of the human brain and that of the macaque brain Schmahmann et al. It will be beneficial to study the precise anatomy of SIPS both in humans and macaques, to integrate the insights from macaque electrophysiology as well as tracer studies Thiebaut de Schotten et al.
As in Uesaki and Ashida , this study employed the functional localiser based on that described in Pitzalis et al. The locations of those regions are consistent with those of the counterparts reported in previous studies Cardin and Smith ; Uesaki and Ashida In some earlier publications Wall and Smith ; Cardin and Smith , ; Uesaki and Ashida , an area identified using optic-flow localisers was referred to as the parieto-insular vestibular cortex PIVC and was considered to be involved in integrating visual and vestibular information to guide self-motion perception.
However, a recent vestibular fMRI study showed that PIVC is selectively responsive to vestibular stimulation, and is unlikely to be activated by visual stimulation Frank et al. Frank et al. Optic flow is a moving pattern on the retina caused by the relative motion between the observer and the scene, and is one of the most important visual cues to the estimation of self-motion Gibson , ; Warren and Hannon However, in most cases, perception of self-motion depends on integration of optic-flow information and signals from other sensory modalities such as the vestibular system.
To understand the neuronal mechanism involved in the estimation of self-motion, it is important to elucidate how the visual and vestibular signals are integrated when we observe optic flow. Previous fMRI studies investigating the cortical areas selective for optic-flow and vestibular stimuli suggest that the sensory areas in the parietal cortex are involved in visuo-vestibular integration necessary for self-motion estimation Wall and Smith ; Cardin and Smith ; Greenlee et al.
Yet, the white matter anatomy that supports the communication amongst those areas has received very little attention in the literature of visual and cognitive neuroscience, even though the existence of SIPS has been known for over a century Sachs ; Vergani et al. One of the biggest advantages of the dMRI-based approach is that the positions of estimated white matter tracts and functionally localised cortical areas can be compared in the brain of the same individual.
This is particularly important to hypothesise the types of information that are transferred via the tracts of interest Kim et al. These cortical areas have been associated with the convergence of visual and vestibular information regarding self-motion Fetsch et al. The spatial relationship between SIPS and the optic-flow selective areas will have implications for interpreting the consequences of white matter lesions that include SIPS, or exploring the neuronal basis of individual differences in self-motion perception.
Our findings show that SIPS is an important structure supporting communication amongst sensory areas in the parietal cortex. It must be noted, however, that it is possible that our results represent only a subset of SIPS. Our tractography results are based on in vivo dMRI data with 1. Tractography based on data with higher resolutions would likely allow for the extraction of a larger portion of SIPS. Likewise, estimation of cortical endpoints would be more accurate with data of better quality, as some cortical endpoints are still missed even with the best dMRI data currently attainable Reveley et al.
It has been suggested that lower b values are not optimal for resolving crossing fibres Tournier et al. To compensate for this limitation, we included HCP data acquired with higher b values, higher spatial and angular resolution from a large number of subjects. Results demonstrated the compelling consistency in the tractography results across the three datasets.
This approach complements the relative disadvantage of the current version of LiFE that it only accepts single-shell data. Contrary to the single-shell approach, multi-shell approaches can be used to generate alternative matrices, which provide additional information regarding tissue microstructures that cannot be captured at a voxel level using single-shell approaches.
It should also be noted that, although SIPS is discussed mainly within the contexts of multisensory integration and optic-flow processing in this article, the SIPS endpoints appear to be near the cortical areas involved in other cognitive functions such as attention Corbetta and Shulman ; Yantis et al. To further understand the implications of SIPS in relation to human behaviour, it may be useful to assess the relationship between individual differences in diffusion properties along SIPS e.
Possible solutions to these limitations include acquiring dMRI data at a higher angular resolution with multiple b values, use of other dMRI techniques e. Future dMRI studies should examine the properties of SIPS in relation to cognitive functions, as well as development and diseases, with consideration to shortcomings of currently available MRI techniques. It is located immediately posterior to the central sulcus and around the intraparietal sulcus; and connects the superior and inferior parts of the parietal cortex.
The location and the trajectory of SIPS are consistent with those observed in post-mortem fibre dissection studies by Sachs and Vergani et al. SIPS was identified consistently across a large number of subjects from three independent dMRI datasets, and the existence of the tract was further corroborated by statistical evidence. These findings place SIPS in a good position to channel neuronal communication between the distant cortical areas underlying visuo-vestibular integration necessary for optic-flow processing and perception of self-motion.
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