Decussation Of Medial Lemniscus

OBJECTIVE: To review the neurologic, neuroradiologic, and electrophysiologic features of autosomal recessive horizontal gaze palsy and progressive scoliosis (HGPPS), a syndrome caused by mutation of the ROBO3 gene on chromosome 11 and associated with defective decussation of certain brainstem neuronal systems.  

AT2 mRNA is detected beginning at E15 in the subthalamic and hypoglossus nuclei; at E17 in the pedunculopontine nucleus, cerebellum, motor facial nucleus, and the inferior olivary complex; at E19 in the thalamus, bed nucleus of the supraoptic decussation, interstitial nucleus of Cajal, nuclei of the lateral lemniscus, locus coeruleus, and supragenual nucleus; and at E21 in the lateral septal and medial amygdaloid nuclei, medial geniculate body, and the superior colliculus.  

Clinical presentation with discrete localization of these lesions suggests that the central taste pathway in humans projects ipsilaterally from the solitary nucleus up to the level of the upper pontine or lower midbrain before decussation. Associated partial sensory disturbance of the face or limb with lack of evidence of medial lemniscus decussation at the upper brainstem suggests that the medial lemniscus may not directly convey taste sensation..  

As judged from relative signal intensities, myelin was present at the post-conceptional age of 30-34 weeks in the following structures: tegmentum pontis (in particular medial lemniscus), superior and inferior colliculi, decussation of the superior cerebellar peduncles, crura cerebri, ventrolateral thalamus, lateral globus pallidus, dorsolateral putamen, dentate nucleus, middle and superior cerebellar peduncles, vermis cerebelli, cortex bordering the central sulcus and hippocampus.  

P30 potential was unaffected while cortical P39 was abnormal in the patients with a supramedullary lesion affecting the somatosensory pathway just above its decussation. Conversely, P30 was abnormal in the presence of a lesion situated caudally to the cervicomedullary junction affecting the lower limb sensory fibers just below their decussation. These clinical observations suggest that P30 potential, as P14 of median nerve somatosensory evoked potentials, is generated in the lower brain stem probably before the decussation of the sensory fibers; nucleus gracilis and medial lemniscus fibers in the lower brain stem are probably the anatomical structures generating P30 potential.  

STT/SHT neurons were antidromically activated with currents < or = 30 microA from the medial lemniscus (ML), anterior pretectal nucleus (APt), posterior nuclear group and medial geniculate nucleus (Po/MG), and zona incerta in the thalamus and from the optic tract (OT), supraoptic decussation, or lateral area of the hypothalamus.  

Some labelled axons were seen coursing to the contralateral side through the posterior commissure and the decussation of the superior cerebellar peduncle.  

Naive and trained rats received unilateral pyramidal sections just rostral to the pyramidal decussation.  

This case provides evidence for the P14 generator being located at the pontine level, in relation to a lemniscal area above the decussation of the somatosensory pathway.  

(ii) III-a, III-b, and III-c originate between the decussation of the medial lemniscus and the thalamus. (iii) PIII probably originates from multiple structures rostral and caudal to the decussation of the medial lemniscus.  

Diencephalic projections to the tectum arise from the ventral lateral geniculate complex ipsilaterally and the ventrolateral nucleus, suprapeduncular nucleus, and nucleus of the ventral supraoptic decussation bilaterally.  

This suggested that both P13 and P14 are generated prior to decussation of the afferent fibres in the medial lemniscus.  

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