Cortex/cortical area

Figure 22.5 Pathways involved in cortico-thalamic synchrony and EEG arousal. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and midbrain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). Its stimulation is followed by EEG arousal. It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state...

Basal ganglia output is directed from GPi and SNr to the thalamus. Movement-related basal ganglia output projects from GPi almost exclusively to the ventrolateral nucleus of the thalamus which, in turn, projects to the primary motor cortex, the cortical supplementary motor area, and other premotor cortical areas. Movement-related output from SNr terminates in the ventral anterior and in... 

A global view of consciousness is that it is generated throughout the entire brain, as a result of synchronisation of relevant neural networks. Specific systems or regions—for example the cerebral cortex, brainstem reticular formation and thalamic nuclei—may be key anatomical integrators. Areas with the most widespread interconnections are pivotal, and on this basis the cortex and thalamus are more relevant than cerebellum and striatum for example. Frontal cortex for example connects with every other brain region, both in terms of input and output, with 80% of such connections accounted for by cortico-cortical connections. Thalamic intralaminar nuclei are, in conjunction with the reticular nucleus, reciprocally connected to all cortical areas. By contrast the cerebellum has very few output pathways and striatal-cortical input is (via the thalamus) confined to frontal lobe. 

The mRNA coding for 5-HT6 receptor has been localized in the rat brain by Northern blot, PCR, and in situ hybridization (206,207,213,214) (see also Fig. 10) and the protein by immunohistochemistry (213). The first and more detailed description on the localization of mRNA coding for 5-HT6 receptor was published by Ward and co-workers (215), reporting that the main rat brain regions where this receptor is expressed is the pyramidal layer of the olfactory tubercle, islands of Calleja, nucleus accumbens, striatum, hippocampus, and piriform cortex. At moderate levels, it is expressed in other cortical areas, the olfactory bulb, some nuclei of the hypothalamus and amygdale, the habenula, and the cerebellum. No mRNA expression is found in the raphe nucleus. These results were confirmed later (204). 

During neonatal development, the brain possesses the striking ability to transfer initially lost functions to new, unaffected cortical areas when irreversible lesions prohibit function of the original representation fields - an ability that is still to a lesser degree present in mature brain. This type of plastic response has been studied in rats with a well defined lesion of the somatosensory cortex that was induced 1 day after birth. Six months later functional MRI (fMRI) was performed with a forepaw stimulation paradigm when the animals showed no neurological... 

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