Probabilistic somatotopy of the spinothalamic pathway at the ventroposterolateral nucleus of the thalamus in the human brain

Disuse-driven plasticity in the human thalamus and putamen

Motor adaptation in cortico-striato-thalamo-cortical loops has been studied mainly in animals using invasive electrophysiology. Here, we leverage functional neuroimaging in humans to study motor circuit plasticity in the human subcortex. We employed an experimental paradigm that combined two weeks of upper-extremity immobilization with daily resting-state and motor task fMRI before, during, and after the casting period. We previously showed that limb disuse leads to decreased functional connectivity (FC) of the contralateral somatomotor cortex (SM1) with the ipsilateral somatomotor cortex, increased FC with the cingulo-opercular network (CON) as well as the emergence of high amplitude, fMRI signal pulses localized in the contralateral SM1, supplementary motor area and the cerebellum. From our prior observations, it remains unclear whether the disuse plasticity affects the thalamus and striatum. We extended our analysis to include these subcortical regions and found that both exhibit strengthened cortical FC and spontaneous fMRI signal pulses induced by limb disuse. The dorsal posterior putamen and the central thalamus, mainly CM, VLP and VIM nuclei, showed disuse pulses and FC changes that lined up with fmri task activations from the Human connectome project motor system localizer, acquired before casting for each participant. Our findings provide a novel understanding of the role of the cortico-striato-thalamo-cortical loops in human motor plasticity and a potential link with the physiology of sleep regulation. Additionally, similarities with FC observation from Parkinson Disease (PD) questions a pathophysiological link with limb disuse.

Thermosensory thalamus: parallel processing across model organisms

The thalamus acts as an interface between the periphery and the cortex, with nearly every sensory modality processing information in the thalamocortical circuit. Despite well-established thalamic nuclei for visual, auditory, and tactile modalities, the key thalamic nuclei responsible for innocuous thermosensation remains under debate. Thermosensory information is first transduced by thermoreceptors located in the skin and then processed in the spinal cord. Temperature information is then transmitted to the brain through multiple spinal projection pathways including the spinothalamic tract and the spinoparabrachial tract. While there are fundamental studies of thermal transduction via thermosensitive channels in primary sensory afferents, thermal representation in the spinal projection neurons, and encoding of temperature in the primary cortical targets, comparatively little is known about the intermediate stage of processing in the thalamus. Multiple thalamic nuclei have been implicated in thermal encoding, each with a corresponding cortical target, but without a consensus on the role of each pathway. Here, we review a combination of anatomy, physiology, and behavioral studies across multiple animal models to characterize the thalamic representation of temperature in two proposed thermosensory information streams.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

Abdominal pain due to the spinothalamic tract injury in patients with mild traumatic brain injury: a case report

Background

We report on a patient with a mild traumatic brain injury (TBI) who developed abdominal pain due to spinothalamic tract (STT) injuries revealed by diffusion tensor tractography (DTT).

Case presentation

A 53-year-old female patient suffered head trauma resulting from a backward fall. While bathing at a public bathhouse, she fell backward and struck the occipital area of her head against the floor. After the head trauma, she experienced pain in the abdomen and in both hands and feet. She underwent evaluations including conventional brain MRI, abdominal and pelvic ultrasonography, and stomach and intestine endoscopy. No abnormality was observed in her brain or abdomen. In addition, her abdominal pain had not been relieved by medical management. When she came to our hospital 4 years after the head trauma, her pain characteristics and severity were as follows: intermittent pain without allodynia or hyperalgesia; squeezing and warm creeping-like pain in the abdomen (visual analog scale score: 7); tingling pain in both hands and feet (visual analog scale score: 7). She was prescribed pregabalin and gabapentin, and her abdominal and limb pain was well-controlled at a tolerable level. On DTT 4 years after head trauma, the upper portion of the spinothalamic tracts (STTs) in both hemispheres showed partial tearing.

Discussion and conclusions

Injury of the STT was demonstrated by using DTT in a patient who showed abdominal pain that was refractory to medical management following mild TBI. Our results suggest that central pain due to STT injury might be suspected in patients with abdominal pain that is refractory to medical management following TBI.

Shifting brain circuits in pain chronicity

The evaluation of brain changes to a specific pain condition in pediatric and adult patients allows for insights into potential mechanisms of pain chronicity and possibly long-term brain changes. Here we focused on the primary somatosensory system (SS) involved in pain processing, namely the ventroposterolateral thalamus (VPL) and the primary somatosensory cortex (SI). We evaluated, using MRI, three specific processes: (a) somatotopy of changes in the SS for different pain origins (viz., foot vs. arm); (b) differences in acute (ankle sprain versus complex regional pain syndrome-CRPS); and (c) differences of the effects of CRPS on SS in pediatric versus adult patients. In all cases, age- and sex-matched individuals were used as controls. Our results suggest a shift in concurrent gray matter density (GMD) and resting functional connectivity strengths (rFC) across pediatric and adult CRPS with (a) differential patterns of GMD (VPL) and rFC (SI) on SS in pediatric vs. adult patterns that are consistent with upper and lower limb somatotopical organization; and (b) widespread GMD alterations in pediatric CRPS from sensory, emotional and descending modulatory processes to more confined sensory-emotional changes in adult CRPS and rFC patterns from sensory-sensory alterations in pediatric populations to a sensory-emotional change in adult populations. These results support the idea that pediatric and adult CRPS are differentially represented and may reflect underlying differences in pain chronification across age groups that may contribute to the well-known differences between child and adult pain vulnerability and resilience.

Interaction of acupuncture treatment and manipulation laterality modulated by the default mode network

Appropriate selection of ipsilateral or contralateral electroacupuncture (corresponding to the pain site) plays an important role in reaching its better curative effect; however, the involving brain mechanism still remains unclear. Compared with the heat pain model generally established in previous study, capsaicin pain model induces reversible cutaneous allodynia and is proved to be better simulating aspects of clinical nociceptive and neuropathic pain. In the current study, 24 subjects were randomly divided into two groups with a 2 × 2 factorial design: laterality (ipsi- or contralateral side, inter-subject) × treatment with counter-balanced at an interval of one week (verum and placebo electroacupuncture, within-subject). We observed subjective pain intensity and brain activations changes induced by capsaicin allodynia pain stimuli before and after electroacupuncture treatment at acupoint LI4 for 30 min. Analysis of variance results indicated that ipsilateral electroacupuncture treatment produced significant pain relief and wide brain signal suppressions in pain-related brain areas compared with contralateral electroacupuncture. We also found that verum electroacupuncture at either ipsi- or contralateral side to the pain site exhibited comparable significant magnitudes of analgesic effect. By contrast, placebo electroacupuncture elicited significant pain reductions only on the ipsilateral rather than contralateral side. It was inferred that placebo analgesia maybe attenuated on the region of the body (opposite to pain site) where attention was less focused, suggesting that analgesic effect of placebo electroacupuncture mainly rely on the motivation of its spatial-specific placebo responses via attention mechanism. This inference can be further supported by the evidence that the significant interaction effect of manipulation laterality and treatment was exclusively located within the default mode network, including the bilateral superior parietal lobule, inferior parietal lobule, precuneus, and left posterior cingulate cortex. It is also proved that disruptions of the default mode network may account for the cognitive and behavioral impairments in chronic pain patients. Our findings further suggested that default mode network participates in the modulation of spatial-oriented attention on placebo analgesia as a mechanism underlying the degree to which treatment side corresponding to the pain.

Delayed-Onset Central Pain due to Degeneration of Ischemic Transcallosal Fibers After Corpus Callosum Hemorrhage

AIMS

A patient developed delayed-onset central pain due to degeneration of the spinothalamic tract resulting from degeneration of the ischemic transcallosal fibers, in the aftermath of a corpus callosum (CC) hemorrhage. The detection and diagnosis of these lesions using diffusion tensor tractography are described.

METHODS

A 59-yr-old man underwent conservative management for hemorrhages in the CC and lateral ventricle that resulted from hitting his head against a wall while falling. He began to feel pain in his right upper and lower extremities approximately 1½ yrs after the initial injury. The pain was characterized as constant tingling, numb, and cool sensation without allodynia or hyperalgesia (visual analogue scale score, 5).

RESULTS

Disruption of transcallosal fibers in the genu and isthmus of the CC was observed on diffusion tensor tractography 1 mo after the initial injury. By 3 yrs, the diffusion tensor tractography showed that transcallosal fibers in the isthmus (67.8%-77.9%) of the CC had disappeared, and the left spinothalamic tract had become thinner.

CONCLUSION

The results suggest that central pain can occur without direct injury of the spinothalamic tract and point up the need for evaluation of the spinothalamic tract and transcallosal fibers in patients with a CC lesion who complain of central pain.

Thalamic Reorganization in Chronic Patients With Intracerebral Hemorrhage: A Retrospective Cross-Sectional Study

The aim of this study was to investigate changes of synaptic area of the spinothalamic tract and its thalamocortical pathway (STT) in the thalamus in chronic patients with putaminal hemorrhage.Twenty four patients with a lesion in the ventral posterior lateral nucleus (VPL) of the thalamus following putaminal hemorrhage were recruited for this study. The subscale for tactile sensation of the Nottingham Sensory Assessment (NSA) was used for the determination of somatosensory function. Diffusion tensor tractography of the STT was reconstructed using the Functional Magnetic Resonance Imaging of the Brain Software Library. We classified patients according to 2 groups: the VPL group, patients whose STTs were synapsed in the VPL; and the non-VPL group, patients whose STTs were synapsed in other thalamic areas, except for the VPL.Thirteen patients belonged to the VPL group, and 8 patients belonged to the non-VPL group. Three patients were excluded from grouping due to interrupted integrity of the STTs. The tactile sensation score of the NSA in the non-VPL group (10.50 ± 0.93) was significantly decreased compared with that of the VPL group (19.45 ± 1.33) (P < 0.05).We found that 2 types of patient had recovered via the VPL area or other areas of the STT. It appears that patients who showed shifting of the thalamic synaptic area of the STT might have recovered by the process of thalamic reorganization following thalamic injury. In addition, thalamic reorganization appears to be related to poorer somatosensory outcome.

Anatomical location of the medial lemniscus and spinothalamic tract at the pons in the human brain: a diffusion tensor tractography study

Using diffusion tensor tractography, we investigated the anatomical location of medial lemniscus (ML) and spinothalamic tract (STT) at pons. We recruited 47 healthy volunteers. Evaluation of the anatomical location of ML and STT was performed using the highest probabilistic location at the upper, middle, and lower pons. According to findings, MLs were located around the middle to medial one-third, between midline and lateral boundary of pons in the pontine tegmentum and STTs were located posterolaterally to ML.

Traumatic thalamic injury demonstrated by diffusion tensor tractography of the spinothalamic pathway

BACKGROUND

This study reports on a patient with traumatic brain injury (TBI) with a thalamic lesion in the ventroposterolateral nucleus which was demonstrated by diffusion tensor tractography (DTT) for the spinothalamic tract and its thalamocortical pathway (STP).

METHODS

One patient with TBI and eight normal control subjects were recruited. A 64-year-old woman who had suffered a motor vehicle accident presented with a persisting tingling sensation and pain in her right upper and lower extremities at 3 weeks after onset. The patient showed impaired touch sensation, but normal proprioception. Diffusion tensor imaging was performed at 1 month after onset. Fractional anisotropy (FA) and mean diffusivity were measured using a region of interest method along the STP.

RESULTS

DTT showed normal STP integrities as compared with normal controls. However, the FA values of the left STP at the thalamus were more than 2 SD decreased. The diminished FA value of the left STP in the left thalamus seems to indicate injury of the left ventrolateroposterior nucleus. Central pain and impaired touch sensation of right extremities supports the presence of left STP injury at the ventroposterolateral nucleus in this patient.

CONCLUSION

It is believed that DTT for the STP provides a useful means of detecting thalamic injury in TBI.