Thalamic infarction disrupts spinothalamocortical projection to the mid-cingulate cortex and supplementary motor area

Diagnostic sensitivity of traumatic axonal injury of the spinothalamic tract in patients with mild traumatic brain injury

Diffusion tensor tractography (DTT) can detect traumatic axonal injury (TAI) in patients whose conventional brain magnetic resonance imaging results are negative. This study investigated the diagnostic sensitivity of TAI of the spinothalamic tract (STT) in patients with a mild traumatic brain injury (TBI) suffering from central pain symptoms, using DTT.Thirty-five patients with central pain following mild TBI and 30 healthy control subjects were recruited for this study. After DTT-based reconstruction of the STT, we analyzed the STT in terms of configuration (narrowing and/or tearing) and the DTT parameters (fractional anisotropy and tract volume).Thirty-three (94.3%) patients had at least 1 DTT parameter value at 1 standard deviation below the control group value, and 20 (57.1%) patients had values at 2 standard deviations, below the control group value. All 35 patients showed STT abnormalities (tearing, narrowing, or both) on DTT.A high diagnostic sensitivity of TAI of the STT in patients with mild TBI was achieved. However, the small number of subjects who visited the university hospital and the limitations of DTT should be considered when generalizing the results of this study.

Alteration of Resting-state Functional Connectivity in the Sensorimotor Network in Patients with Thalamic Infarction

PURPOSE

To explore changes in functional connectivity (FC) within the sensorimotor network (SMN) and the relationship between the SMN and bilateral thalamus in patients with thalamic infarction (TI) using resting state functional magnetic resonance imaging (rs-fMRI). Also determined was whether those measures are useful for monitoring the functional recovery of somatosensory deficits.

METHODS

The study included 31 patients with TI presenting somatosensory dysfunction and 31 controls who underwent clinical assessments and MRI scanning at 6 months after a stroke. An independent component analysis was used to identify the SMN. The mean time courses of SMN activity were extracted for each subject, and FC with the bilateral thalamus was assessed. Differences in connectivity strength were compared between groups. Finally, we correlated the altered FC values with clinical data from patients with TI.

RESULTS

Compared to controls, patients with TI showed decreases in FC within SMN in the ipsilesional posterior central gyrus (PCG) (Z-score = -4.581, cluster size = 171), but presented increased FC within the SMN in the ipsilesional supplementary motor area (SMA) (Z-score = 4.648, cluster size = 46). The FC values of the ipsilesional SMA correlated with the somatosensory function score of patients with TI (r = 0.426, P = 0.027). Increased FC was observed between the SMN and bilateral thalamus in patients with TI. The region exhibiting increased FC was adjacent to the lesion in the affected thalamus, while the area with increased FC overlapped the location of the lesion when the lesion was mirrored onto the unaffected thalamus.

CONCLUSION

The increased FC in the ipsilesional SMA and between the SMN and perilesional thalamus might reflect functional reorganization in patients with TI presenting somatosensory deficits.

Different Patterns of Functional Connectivity Alterations Within the Default-Mode Network and Sensorimotor Network in Basal Ganglia and Pontine Stroke

Background

The aim of this study was to investigate whether patients with basal ganglia stroke and patients with pontine stroke have different types of functional connectivity (FC) alterations in the early chronic phase.

Material/Methods

We included 14 patients with pontine stroke, 17 patients with basal ganglia stroke, and 20 well-matched healthy controls (HCs). All of them underwent resting-state functional magnetic resonance imaging (rs-fMRI) scanning. The independent component analysis (ICA) approach was applied to extract information regarding the default-mode network (DMN), including anterior DMN (aDMN) and posterior DMN (pDMN) components and the sensorimotor network (SMN).

Results

Compared with HCs, patients with basal ganglia stroke exhibited significantly reduced FC in the left precuneus of the pDMN, right supplementary motor area (SMA), and right superior frontal gyrus (SFG) of the SMN. Additionally, FC in the left medial prefrontal gyrus (MFG) of the aDMN, right precuneus and right posterior cingulate cortex (PCC) of the pDMN, and left middle cingulate gyrus (mid-CC) of the SMN decreased in patients with pontine stroke.

Conclusions

The different patterns of FC damage in patients with basal ganglia stroke and patients with pontine stroke in the early chronic phase may provide a new method for investigating lesion-induced network plasticity.

Effects of thalamic infarction on the structural and functional connectivity of the ipsilesional primary somatosensory cortex

OBJECTIVES

To identify regions causally influenced by thalamic stroke by measuring white matter integrity, cortical volume, and functional connectivity (FC) among patients with thalamic infarction (TI) and to determine the association between structural/functional alteration and somatosensory dysfunction.

METHODS

Thirty-one cases with TI-induced somatosensory dysfunction and 32 healthy controls underwent magnetic resonance imaging scanning. We reconstructed the ipsilesional central thalamic radiation (CTR) and assessed its integrity using fractional anisotropy (FA), assessed S1 ipsilesional changes with cortical volume, and identified brain regions functionally connected to TI locations and regions without TI to examine the potential effects on somatosensory symptoms.

RESULTS

Compared with controls, TI patients showed decreased FA (F = 17.626, p < 0.001) in the ipsilesional CTR. TI patients exhibited significantly decreased cortical volume in the ipsilesional top S1. Both affected CTR (r = 0.460, p = 0.012) and S1 volume (r = 0.375, p = 0.049) were positively correlated with somatosensory impairment in TI patients. In controls, the TI region was highly functionally connected to atrophic top S1 and less connected to the adjacent middle S1 region in FC mapping. However, T1 patients demonstrated significantly increased FC between the ipsilesional thalamus and middle S1 area, which was adjacent to the atrophic S1 region.

CONCLUSIONS

TI induces remote changes in the S1, and this network of abnormality underlies the cause of the sensory deficits. However, our other finding that there is stronger connectivity in pathways adjacent to the damaged ones is likely responsible for at least some of the recovery of function.

KEY POINTS

• TI led to secondary impairment in the CTR and cortical atrophy in the ipsilesional top of S1. • TI patients exhibited significantly higher functional connectivity with the ipsilateral middle S1 which was mainly located within the non-atrophic area of S1. • Our results provide neuroimaging markers for non-invasive treatment and predict somatosensory recovery.

Independent component analysis of functional networks for response inhibition: Inter-subject variation in stop signal reaction time

Cognitive control is a critical executive function. Many studies have combined general linear modeling and the stop signal task (SST) to delineate the component processes of cognitive control. For instance, by contrasting stop success (SS) and stop error (SE) trials in the SST, investigators examined regional responses to stop signal inhibition. In contrast to this parameterized approach, independent component analysis (ICA) elucidates brain networks subserving cognitive control. In our earlier work of 59 adults performing the SST during fMRI, we characterized six independent components (ICs). However, none of these ICs correlated with stop signal performance, raising questions about their behavioral validity. Here, in a larger sample (n = 100), we identified and explored 23 ICs for correlation with the stop signal reaction time (SSRT), a measure of the efficiency of response inhibition. At a corrected threshold (P < 0.0005), a paracentral lobule-midcingulate network and a left inferior parietal-supplementary motor-somatomotor network showed a positive correlation between SE beta weight and SSRT. In contrast, a midline cerebellum-thalamus-pallidum network showed a negative correlation between SE beta weight and SSRT. These findings suggest that motor preparation and execution prolongs the SSRT, likely via an interaction between the go and stop processes as suggested by the race model. Behaviorally, consistent with this hypothesis, the difference in G and SE reaction times is positively correlated with SSRT across subjects. These new results highlight the importance of cognitive motor regions in response inhibition and support the utility of ICA in uncovering functional networks for cognitive control in the SST.

Anatomical correlates of proprioceptive impairments following acute stroke: a case series

BACKGROUND

Proprioception is the sensation of position and movement of our limbs and body in space. This sense is important for performing smooth coordinated movements and is impaired in approximately 50% of stroke survivors. In the present case series we wanted to determine how discrete stroke lesions to areas of the brain thought to be critical for somatosensation (thalamus, posterior limb of internal capsule, primary somatosensory cortex and posterior parietal cortex) would affect position sense and kinesthesia in the acute stages post-stroke. Given the known issues with standard clinical measures of proprioception (i.e. poor sensitivity and reliability) we used more modern quantitative robotic assessments to measure proprioception.

METHODS

Neuroimaging (MRI, n=10 or CT, n=2) was performed on 12 subjects 2-10 days post-stroke. Proprioception was assessed using a KINARM robot within the same time frame. Visually guided reaching was also assessed to allow us to compare and contrast proprioception with visuomotor performance.

RESULTS AND CONCLUSIONS

Proprioceptive impairments were observed in 7 of 12 subjects. Thalamic lesions (n=4) were associated with position sense (n=1) or position sense and kinesthesia (n=1) impairments. Posterior limb of the internal capsule lesions (n=4) were associated with primarily position sense (n=1) or kinesthesia (n=2) impairments. Lesions affecting primary somatosensory cortex and posterior parietal cortex (n=2) were associated with significant position sense and kinesthesia impairments. All subjects with damage to hypothesized structures displayed impairments with performance on the visually guided reaching task. Across the proprioceptive tasks, we saw that position sense and kinesthesia were impaired to differing degrees, suggesting a potential dissociation between these two components of proprioception.

The cortical activation pattern by a rehabilitation robotic hand: a functional NIRS study

Introduction: Clarification of the relationship between external stimuli and brain response has been an important topic in neuroscience and brain rehabilitation. In the current study, using functional near infrared spectroscopy (fNIRS), we attempted to investigate cortical activation patterns generated during execution of a rehabilitation robotic hand.

Methods: Ten normal subjects were recruited for this study. Passive movements of the right fingers were performed using a rehabilitation robotic hand at a frequency of 0.5 Hz. We measured values of oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR) and total-hemoglobin (HbT) in five regions of interest: the primary sensory-motor cortex (SM1), hand somatotopy of the contralateral SM1, supplementary motor area (SMA), premotor cortex (PMC), and prefrontal cortex (PFC).

Results: HbO and HbT values indicated significant activation in the left SM1, left SMA, left PMC, and left PFC during execution of the rehabilitation robotic hand (uncorrected, p < 0.01). By contrast, HbR value indicated significant activation only in the hand somatotopic area of the left SM1 (uncorrected, p < 0.01).

Conclusions: Our results appear to indicate that execution of the rehabilitation robotic hand could induce cortical activation.