Neurological Examination, clinical cases and neuropsychological ...

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23/07/54 The Human Reticular Formation: Reticular Functions: ‐ Integration of Sensory and motor functions ‐ Control of states of consciousness Waking, Sleep, Dream, Altered States ‐ Control of behavioural states ‐ Arousal, Attention, Orienting, Habituation ‐ Sensory filtering (“The Cocktail Party Effect”) ‐ Motor functions: Postural Controls Eye movements: Gaze, Saccade, REM ‐ Autonomic controls: respiration, heart rates, blood pressure ARAS: Ascending Reticular Activating System 415703 Cognitive Neuropsychology Week 4: The occipital 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 occipital lobes and their functions 2. The Visual System 3. Visual Perception and Visual Cortical Organization 4. The two Stream Hypothesis: The Dorsal stream, “Where or How” and The Ventral Stream, “What” 5. Neuropsychology of the Occipital lobes. 28
23/07/54 Occipital lobe Vision processing The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1 (visual one). Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the posterior pole of the occipital lobe. V1 is often also called striate cortex because it can be identified by a large stripe ti of myelin, the Striaof Gennari. Visually driven di regions outside V1 are called extrastriate cortex. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color discrimination and motion perception. The name derives from the overlying occipital bone, which is named from the Latin oc‐ + caput, "back of the head". Functions of the Occipital lobes: Significant functional aspects of the occipital lobe is that it contains the primary visual cortex and is the part of the brain where dreams come from. Retinal sensors convey stimuli through the optic tracts to the lateral geniculate bodies, where optic radiations continue to the visual cortex. Each visual cortex receives raw sensory information from the outside half of the retina on the same side of the head and from the inside half of the retina on the other side of the head. The cuneus (Brodmann's area 17) receives visual information from the contralateral superior retina representing the inferior visual field. The lingula receives information from the contralateral inferior retina representing the superior visual field. The retinal inputs pass through a "way station" in the lateral geniculate nucleus of the thalamus before projecting to the cortex. Cells on the posterior aspect of the occipital lobes' gray matter are arranged as a spatial map of the retinal field. Functional neuroimaging reveals similar patterns of response in cortical tissue of the lobes when the retinal fields are exposed to a strong pattern. If one occipital lobe is damaged, the result can be homonomous vision loss from similarly positioned "field cuts" in each eye. Occipital lesions can cause visual hallucinations. Lesions in the parietal‐temporal‐occipital association area are associated with color agnosia, movement agnosia, and agraphia. The occipital lobe is divided into several functional visual areas. Each visual area contains a full map of the visual world. Although there are no anatomical markers distinguishing these areas (except for the prominent striations in the striate cortex), physiologists have used electrode recordings to divide the cortex into different functional regions. The first functional area is the primary visual cortex. It contains a low‐level description of the local orientation, spatial‐frequency and color properties within small receptive fields. Primary visual cortex projects to the occipital areas of the ventral stream (visual area V2 and visual area V4), and the occipital areas of the dorsal stream—visual area V3, visual area MT (V5), and the dorsomedial area (DM). 29
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