Neurological Examination, clinical cases and neuropsychological ...

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23/07/54 The fusiform face area (FFA) is a part of the human visual system which might be specialized for facial recognition, although there is some evidence that it also processes categorical information about other objects, particularly familiar ones. Localization The FFA is located in the ventral stream on the ventral surface of the temporal lobe on the fusiform gyrus. It is adjacent to the parahippocampal place area and near the putative extrastriate body area. It is in a slightly different place for each human and displays some lateralization, usually being larger in the right hemisphere. The FFA was discovered and continues to be investigated in humans using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies. Usually, a participant views images of faces, objects, places, bodies, scrambled faces, scrambled objects, scrambled places and scrambled bodies. This is called a functional localizer. Comparing the neural response between faces and scrambled faces will reveal areas that are faceresponsive, while comparing cortical activation between faces and objects will reveal areas that are face‐selective. Functional role The human FFA was first described by Justine Sergent in 1992 and more recently by Nancy Kanwisher in 1997 who proposed that the existence of the FFA is evidence for domain specificity in the visual system. More recently, it has been suggested that the FFA processes more than just faces. Some groups, including Isabel Gauthier and others, maintain that the FFA is an area for recognizing fine distinctions between well‐known objects. Gauthier et al. tested both car and bird experts, and found some activation in the FFA when car experts were identifying cars and when bird experts were identifying birds. A recent paper by Kalanit Grill‐Spector et al. also suggests that processing in the FFA is not exclusive to faces, although an erratum was later published which brought to light some errors.The debate about the functional role of the FFA is ongoing. A 2009 magnetoencephalography study found that objects incidentally perceived as faces, an example of pareidolia, evoke an early (165 ms) activation in the FFA, at a time and location similar to that evoked by faces, whereas other common objects do not evoke such activation. This activation is similar to a slightly earlier peak at 130 ms seen for images of real faces. The authors suggest that face perception evoked by face‐like objects is a relatively early process, and not a late cognitive reinterpretation phenomenon. Fusiform Face Area (FFA) N & NJ Kotchabhakdi 2008 260 Prosopagnosia (Greek: "prosopon" = "face", "agnosia" = "inabilty to recognise/identify familiar people or objects") is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. The term originally referred to a condition following acute brain damage, but a congenital form of the disorder has been proposed, which may be inherited by about 2.5% of the population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus. Few successful therapies have so far been developed for affected people, although individuals often learn to use 'piecemeal' or 'feature by feature' recognition strategies. This may involve secondary clues such as clothing, gait, hair color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others. Some also use the term prosophenosia, which refers to the inability to recognize faces following extensive damage of both occipital and temporal lobes 415703 Cognitive Neuropsychology Week 6: The Frontal lobes Naiphinich Kotchabhakdi, Ph.D. Director, Salaya Stem Cell R & D Project, Research Center for Neuroscience, Institute of Molecular Biosciences, Mahidol University Salaya Campus, 999 Phutthamonthol 4 Road, Salaya, Phutthamonthol, Nakornpathom 73170 Thailand Email: scnkc@mahidol.ac.th or naiphinich@gmail.com Web: www.neuroscience.mahidol.ac.th Main Objectives: 1. The Frontal lobes and their functions 2. The Motor System 3. Motor Cortical Organization in the Frontal Lobe 4. The Prefrontal cortex 5. The Frontal lobes and higher or executive brain functions 6. Deep brain structures in Frontal lobe, e.g., Limbic brain structures and their functions 7. Neuropsychology of the Frontal lobes and executive brain function disorders. 44
23/07/54 The Frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to (in front of) the parietal lobes and superior and anterior to the temporal lobes (i.e. directly behind the forehead or "temple"). It is separated from the parietal lobe by the post‐central gyrus primary motor cortex, which controls voluntary movements of specific body parts associated with the precentral gyrus posteriorly, inferiorly by lateral sulcus[slyvian] which separates it from the temporal lobe, superiorly by the superior margin of the hemisphere and anteriorly by the frontal pole. The frontal lobe contains most of the dopamine‐sensitive neurons in the cerebral cortex. The dopamine system is associated with reward, attention, short‐term term memory tasks, planning, and drive. Dopamine tends to limit and select sensory information arriving from the thalamus to the fore‐brain. A report from the National Institute of Mental Health says a gene variant that reduces dopamine activity in the prefrontal cortex is related to poorer performance and inefficient functioning of that brain region during working memory tasks, and to slightly increased risk for schizophrenia. Frontal lobe Anatomy On the lateral surface of the human brain, the central sulcus separates the frontal lobe from the parietal lobe. The lateral sulcus separates the frontal lobe from the temporal lobe. The frontal lobe can be divided into a lateral, polar, orbital (above the orbit; also called basal or ventral), and medial part. Each of these parts consists of particular gyri: ∆ Lateral part: Precentral gyrus, lateral part of the superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus. ∆ Polar part: Transverse frontopolar gyri, frontomarginal gyrus. ∆ Orbital part: Lateral orbital gyrus, anterior orbital gyrus, posterior orbital gyrus, medial orbital gyrus, gyrus rectus. ∆ Medial part: Medial part of the superior frontal gyrus, cingulate gyrus. The gyri are separated by sulci. E.g., the precentral gyrus is in front of the central sulcus, and behind the precentral sulcus. The superior and middle frontal gyri are divided by the superior frontal sulcus. The middle and inferior frontal gyri are divided by the inferior frontal sulcus. In humans, the frontal lobe reaches full maturity around only after the 20s, marking the cognitive maturity associated with adulthood. Dr. Arthur Toga, a UCLA professor of neurology, found increased myelin in the frontal lobe white matter of young adults compared to that of teens. A typical onset of schizophrenia in early adult years correlates with poorly myelinated and thus inefficient connections between cells in the fore‐brain Pyramidal motor system: Corticospinal tracts tracts is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord. The corticospinal tract mostly contains motor axons. It actually consists of two separate tracts in the spinal cord: the lateral corticospinal tract and the anterior corticospinal tract. An understanding of these tracts leads to an understanding of why for the most part, one side of the body is controlled by the opposite side of the brain. The corticobulbar tract is also considered to be a pyramidal tract, though it carries signals to motor neurons of the cranial nerve nuclei, rather than the spinal cord. The neurons of the corticospinal tracts are referred to as pyramidal neurons. The name comes from the shape of the corticospinal tracts, which somewhat resemble pyramids as they pass through the medulla. The corticospinal tract is concerned specifically with discrete voluntary skilled movements, especially of the distal parts of the limbs. (Sometimes called "fractionated" movements) The motor pathway The corticospinal tract originates from pyramidal cells in layer V of the cerebral cortex. About half of its fibres arise from the primary motor cortex. Other contributions come from the supplementary motor area, premotor cortex, somatosensory cortex, parietal lobe, and cingulate gyrus. The average fiber diameter is in the region of 10μm; around 3% of fibres are extra‐large (20μm) and arise from Betz cells, mostly in the leg area of the primary motor cortex. Upper motor neurons The neuronal cell bodies in the motor cortex, together with their axons that travel down through the brain stem and spinal cord are commonly referred to as upper motor neurons. It should be noted however, that they do not project to muscles, and thus the term 'motor neuron' is somewhat misleading. Anatomy of the motor cortex The motor cortex can be divided into four main parts: ∆ the primary motor cortex (or M1, Broadman area #4), responsible for generating the neural impulses controlling execution of movement and the secondary motor cortices, including ∆ the posterior parietal cortex, responsible for transforming visual information into motor commands ∆ the premotor cortex, (Broadman areas #6, 8, 9,10) responsible for motor guidance of movement and control of proximal and trunk muscles of the body ∆ and the supplementary motor area (or SMA), responsible for planning and coordination of complex movements such as those requiring two hands. Other brain regions outside the cortex are also of great importance to motor function, most notably the cerebellum and subcortical motor nuclei. 45
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