Cerebral cortex lobes

The temporal lobe is the inferior middle portion of the cerebral cortex of both hemispheres. The temporal lobes are involved in the analysis of visual and acoustic information and in memory formation. The hippocampus is part of the inner, medial side of the temporal lobes. 

Textbooks on neuroscience often describe the location and function of hundreds of individual brain regions (see references above). However, for current purposes these will be kept to a minimum (Figure 2.1). Anatomically, the brain can be subdivided into the forebrain containing the telencephalon and diencephalon, the midbrain or mesencephalon and the hindbrain (metencephalon and myelencephalon). The telencephalon includes the left and right cerebral hemispheres encompassed by the cerebral cortex (neocortex). Cortex is a translation of the word bark and is so-called because its surface, made up of numerous sulci (grooves or invaginations) and gyri (raised areas), is on the outer surface of the brain like the bark of a tree. Each hemisphere is divided into four lobes, named from the front (rostral) to back (caudal) of the brain frontal, temporal, parietal and occipital. 

Frontotemporal dementias occur as familial forms and, more commonly, as sporadic diseases. They are characterized by a remarkably circumscribed atrophy of the frontal and temporal lobes of the cerebral cortex, often with additional, subcortical changes. In 1994, an autosomal-dominantly inherited form of frontotemporal dementia with parkinsonism was linked to chromosome 17q21.2. Subsequently, other forms of frontotemporal dementia were linked to this region, resulting in the denomination frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) for this class of disease. All cases of FTDP-17 have so far shown a filamentous pathology made of hyperphosphorylated tau protein (Fig. 45-7). In 1998, mutations in tau were reported in FTDP-17 patients [29-31]. Since then, more than 30 different mutations have been described in over 80 families with FTDP-17 (Fig. 45-6). 

The cerebrum is composed of four lobes covered by cerebral cortex frontal, parietal, temporal, and occipital (figure 2.9). The cortical surface... 

CYP26A1 mRNA in human cerebellum, less in cerebral cortex, medulla, occipital pole, frontal lobe, and temporal lobe (White et al., 2000). 

The cerebral cortex is conventionally subdivided into four main regions that may be delineated by the sulci, or large clefts, termed the frontal, temporal, parietal and occipital lobes. These names are derived from the bones of the skull which overlay them. Each lobe may be further subdivided according to its cellular structure and composition. Thus Brodmarm has divided the cortex into approximately 50 discrete areas according to the specific cellular structure and function. For example, electrical stimulation of the strip of cerebral cortex in front of the central sulcus (see Figure 1.3) is responsible for motor commands to the muscles. This is termed the primary motor cortex and can be further subdivided according to which muscles are controlled in different parts of the body. 

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. 

Dopamine receptors include at least 4 subtypes which are concentrated in the striatum where D1 and D2 are evenly distributed and D3 is concentrated in the limbic portion, nucleus accumbens (Herroelen et al., 1994). D2 but not D1 receptors also occur throughout the cerebral cortex particularly temporal lobe, and D3 receptors are also present in lower densities in hippocampus and amygdala. D3 receptors are localised in several thalamic nuclei including the lateral geniculate, mediodorsal and anteroventral. 

VIP is a neurotransmitter in the cerebral cortex, the hypothalamus, amygdala, hippocampus, corpus striatum, and the vagal nuclei of the medulla oblongata (131,132). VIP receptors are widely distributed in cerebral cortex, amygdaloid nuclei, hippocampus, olfactory lobes, thalamus, and the suprachias-matic nucleus, and are present in lower concentrations in the hippocampus, brainstem, spinal cord, and dorsal root ganglia. VIP is also involved in the release of other hormones such as CRH, PRL, oxytocin, and vasopressin. 

GABA (gamma- aminobutyric acid) Inhibitory. Secreted by neurons in the cerebral cortex, subcortical area, and spinal cord. Anxiety states, also involved in chemical dependency. Diffusely affected by many medications. Many antianxiety medications work on GABA receptor sites, especially in the frontal lobe of the brain. Alcohol, benzodiazepines, and barbiturates all affect GABA receptors, as do other drugs. 

The visual cortex occupies the occipital and parts of the parietal and temporal lobes of the cerebral cortex. Like the entire cortex, it forms a highly folded structure, with a thickness of approximately 1.5 mm. It is surrounded by the cerebrospinal fluid, several layers of meninges- pia mater, arachnoid, dura, and the skull. 

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