Neurophysiology of the Migraine Brain by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030565381
Publisher: Springer International Publishing

9.3.4 Somatosensory Temporal Discrimination

The ability to distinguish two identical somaesthetic stimuli applied to the same spot or different cutaneous regions in short intervals is referred to as somatosensory temporal discrimination (STD) [13]. It is crucial for somatosensory functions such as kinesthesia, graphesthesia, and stereognosis [89, 90]. The somatosensory temporal discrimination threshold (STDT) is defined as the shortest delay between two stimuli that still allows discrimination and differs between body areas [13].

Different studies evaluated STD in migraine patients [14–16]. Boran and colleagues examined the STDTs of the upper extremity (dermatome C7) and face (mandibular nerve) in patients with episodic migraine and healthy volunteers. While no difference could be found interictally, an approximately two- to fourfold prolongation was observed in all regions during an attack [14]. In the contralateral upper extremity and the ipsilateral face, STDTs were significantly longer compared to other regions. These prolongations were thought to have resulted from alterations of central pain perception. However, it has been suggested that a significant prolongation of the contralateral upper extremity and ipsilateral face cannot be explained by the impairment of sensory networks alone [14].

In patients with chronic migraine (CM), STDTs are approximately three times longer than in healthy volunteers—even on days without headache. This finding stands in contrast to episodic migraine where normal interictal STDTs were found. This suggests that the impairment of sensorial processing is sustained in chronic migraine [15]. Again, patients with chronic migraine seem to be locked in an ictal state. In patients with tension-type headache (TTH), on the other hand, STDTs are unaltered [16]. Therefore, STD may be used as a biomarker for chronic migraine as well as to differentiate migraine from TTH [15, 16].

Abnormal STD does not only occur in migraine; it has been linked to cerebral damage in different locations. Lesions in the primary somatosensory cortex, the internal capsule, and the thalamus may cause impairment of both sensory perception and STD. Lesions in the posterior parietal cortex, head of the caudate nucleus, putamen, medial thalamus, and lenticular nucleus do not affect sensory perception but lead to abnormal STD. Finally, a bilateral lesion of the supplementary motor area may be associated with impaired STD as well [91]. In healthy subjects, fMRI imaging revealed the inferior parietal lobule, the middle and inferior frontal gyrus, the anterior part of the right insula, the right anterior cingulate gyrus, as well as the cerebellum to be relevant for STD. The pre-SMA and the anterior cingulate gyrus are thought to be specific for the task [92].

Higher STDTs also occur in patients suffering from movement disorders such as Parkinson’s disease, dystonia, and multisystem atrophy [93, 94]. Consequently, basal ganglia are likely to play an important role in temporal discrimination. The affection of STD in Parkinson’s disease is thought to be due to an impairment of sensorimotor integration, timing, and projections to the supplementary motor area [95]. Finally, STDTs are higher in patients with cerebellar atrophy [96].

Some of the structures involved in pain perception during migraine attacks such as the insula, cingulate gyrus, cerebellum, and basal ganglia are known to play a role in STD impairment [97].

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