What do we mean by functional specialization of the cortex - Essay Example

?What do we mean by "functional specialization" of the cortex? Define this concept and discuss two different examples of functional specialization. Introduction Functional specialization basically refers to the biological phenomenon whereby different parts of the brain become specialized to perform specific functions. In general, the theory of modularity and distributive processing seek to explain brain functioning. Modularity suggests that the brain has various modules which have specific domains in terms of functioning. On the other hand, distributive processing indicates that the brain is very much interactive with its various regions connected, not specialized. In following the theory of modularity, there would be areas of the brain which are functionally specialized and domain-specific for certain cognitive functions (Caramazza and Coltheart, 2006). This domain-specific functioning is a result of the natural changes in human biology. Domain specificity has a significant role in the development of cognition as it often helps identify adaptive issues (Caramazza and Coltheart, 2006). This paper shall now discuss what functional specialization of the cortex means. It shall define the concept and discuss two different examples of functional specialization. Body Functional specialization has been first analysed in the 1860s as Broca of France as well as Fritsch and Hitzig from Germany established the basis of functional specialization by identifying the integrity of specific cortical regions needed for articulate speech as well as voluntary muscle movement (Zeki, et.al., 1991). Work relating to the charting of the various cortical areas relate to numerous functions. The functional specialization of a specific cortical region is based mostly on manifestations of connectivity, with functional segregation calling for cells with similar qualities to be lumped together (Zeki, et.al., 1991). The external interactions between the cortical regions are not continuous, but mostly manifest in patches. Such pattern, in some instances has a known relationship with functional segregation. The centralized management of cortical processing is based on the distinction between the forward and the backward link which mostly refers to the cortical layers of origin and then termination (Friston, et.al., 2011). The forward connections are focusing on connections which bring the target neurons to a predetermined response on the basis of inputs, and are also involved in the separation of sensory data. The qualities of specialisation are important in some areas of neuroscience and secure an infrastructure where normal brain functions can be understood. (Friston, et.al., 2011) The functional roles which are carried out by various regions of the brain are based on its varying connections. Some aspects of cortical projections are so common that they are tantamount to elements of connectivity (Friston, et.al., 2011). These rules are based on functional specialization. Where neurons in a specific area share common responsiveness to sensorimotor or cognitive elements, then the specialisation is also anatomical (Zysset, et.al., 2002). Functional specialization calls for cells performing similar functions lumped together. The structural limitations call for convergence and divergence of the cortical links (Craighead and Nemeroff, 2004). The external connections of the cortical areas are not continuous, but they manifest in clusters. Such clusters are related to functional specialisation. For instance, a visual region located at the back of the brain (V2) has a specific cytochrome oxidase staining pattern made up of thick stripes, thin stripes, and then interstripes (Craighead and Nemeroff, 2004). When patters are recorded for V2, directionally selective neurons are seen exclusively in the thick stripes. The retrograde designation of cells in an area sharing similar functions is also seen (Zielasek and Gaeble, 2008). There are various examples of functional specialization, one of the most well known examples being the specialization of the fusiform face area (FFA) (Kanwisher, et.al., 1997). Researcher Sergent was one of the researchers who established evidence on functional specialization with observations made on varying patterns of activation for different activities – face processing and object processing (Sergent and Signoret, 1992). Patients with lesions on the occipital and temporal lobes were studied and it was soon revealed that impairments in face processing manifested, but not on the recognition of regular objects. The area known as the inferior temporal cortex also appeared more active than other areas of the brain when the subjects attempted to recognize and classify faces (Sergent and Signoret, 1992). In effect, their study established proof supporting the domain-specific qualities seen in the visual system, with the FFA indicated specifically for facial perception and recognition. Within the visual cortex, functional specialization was also observed. Semi Zeki et al (1991) was able to identify regions which specifically functioned to perceive colour and vision motion. The visual area V4 was identified as specialized towards colour and seen when subjects viewed two identical images, one being of different colour and the other in shades of grey (Zeki, et.al., 1991). This is supported by other lesion studies for subjects who could not see the colours following trauma to the v4 area (Pearlman, et.al., 1979). Considering imaging tests like PET and MRI, subjects asked to look at moving checker board patterns and then stationary checker board patterns allowed for the identification of visual area v5 which was specialized for vision motion (Watson, et.al., 1993). Such aspect of functional specialization was also seen in the study by Zihl and colleagues (1983) where identified lesions in the v5 area manifested affectations relating to cerebral motion blindness. The idea of functional specialization for the visual cortex was seen in 1970s studies. It is founded on studies of the macaque monkey which manifest that with various visual areas which are beyond the striate cortex, one area is specified for visual motion, another for colour (Cragg, 1969). Based on this finding, stronger attempts have been secured in the establishment of specific visual aspects of the brain. In the study by Duncan and Owen (2000), the frontal lobes are specialized towards higher level cognitive processes. As such, the controls refer to coordination, planning, and the organization of actions relating to individual goals. This relates to matters like behaviour, language, and reasoning (Duncan and Owen, 2000). The prefrontal cortex specifically functions towards these areas, especially on executive control processes including decision-making, correction of errors, and reversing habitual responses (Duncan and Owen, 2000). The study by Miller and Cummings (2007) utilised PET and functional MRI in order to support memory functions in the left frontal cortex as well as the visuospatial working memory within the right frontal cortex. The authors also indicate that in instances where patients with left frontal lobe patients were observed, they manifested issues in the control of executive activities including the conceptualization of strategies (Miller and Cummings, 2007). The dorsolateral, ventrolateral, and anterior cingulated areas in the prefrontal cortex are said to function together in accomplishing cognitive activities, often related to interaction theories. However, much evidence has been seen indicating specific specializations in this network (Duncan and Owen, 2000). Miller and Cummings (2007) also observed that the dorsolateral prefrontal cortex is concerned with the manipulation and monitoring of sensorimotor data for working memory. Functional specialization can also be explained through specialisations seen in the corpus callosum. In an experiment carried out by Roger Sperry (in Schacter, et.al., 2011), the authors evaluated epileptic patients with cut corpus callosum. The experiment used flashing images in the right and left visual fields for the research subjects. With the cut corpus callosum, information gathered by the right field was not transmitted to the left hemisphere, and vice versa. Most participants were fully able to repeat when image they saw, but when asked to draw the image, they could not (Schacter, et.al., 2011). When the image was flashed in the left visual field, the data was sent to the right hemisphere, but when asked to repeat what they have seen, they were not able to remember the image presented, but were able to draw the image. Sperry therefore established that the left hemisphere is focused on language, especially as participants are able to speak about the image they saw; however, the right hemisphere related to creative functions, including drawing (Schacter, et.al., 2011) The parahippocampal place area (PPA) was established by Nancy Kanwisher and Russell Epstein (1998) following an fMRI study which indicated that PPA allows for immediate favourable response to scenes which include spatial layout, and minimally to singular objects, and then not at all to faces. The study also established that the PPA records places by noting the geometry of the local environment (Epstein and Kanwisher, 1998). Moreover, Park and Chun (2009) also propose that the activation of the PPA is based specifically on viewpoint; as such, it reacts to shifts in the angles of the image viewed. On the other hand, the retrosplenial cortex (RSC) is not specific to viewpoint angles and does not change its level of reaction when changes in angles are made (Park and Chun, 2009). This would indicate supportive arrangements in functions not found within visual processing brain regions. The extrastriate body area, otherwise known as the EBA is found in the lateral occipital cortex. Based on fMRI studies, this area has functional specialization relating to subjects viewing human bodies or parts of the body (Downing, et.al., 2001). The EBA does not function well in reacting to objects of parts of an object, but responds well enough to human bodies and its parts. The study by Downing, et.al., (2001), respondents to an experiment were asked to view a series of images. Such images included objects, parts of objects, the human body in various positions and in various details, and also body parts. The experiment revealed more activation or a stronger response to images of human bodies, regardless of extent of detail, as compared to parts of body or parts of objects (Downing, et.al., 2001). Conclusion In general therefore, the functional specialization of the brain refers to groupings in the brain which cluster in order to carry out specific and highly specialized functions. Such specialization is based on functional modalities which are enhanced in some respects. Various kinds of functional specialization include specializations in the visual cortex, in the FFA, the frontal lobes relating to higher cognitive functions, and among others, specialization in the corpus callosum. These specializations allow for perception and reactions to be more unique to specific functions and manifestations. These specializations also relate to improved functions for certain individuals regarding certain frameworks. In the end, the specializations portray diverse and dynamic brain functions, allowing certain behaviours to manifest and thrive. References Caramazza, A. & Coltheart, M. (2006). Cognitive neuropsychology twenty years on. Psychology Press, 23(1): 3–12. Cragg, B. (1969). The topography of the afferent projections in circumstriate visual cortex (C.V.C.) of the monkey studied by the Nauta method. Vision Res, 9:733-747. Craighead, W. & Nemeroff, C. (2004). The concise corsini encyclopedia of psychology and behavioral science. London: John Wiley & Sons. Downing, P., Jiang, Y., Shuman, M. & Kanwisher, N. (2001). A cortical area selective for visual processing of the human body. Science, 293 Duncan, J., & Owen, A. (2000). Common regions of the human frontal lobe recruited by diverse cognitive demands. London: Elsevier Science Epstien, R., & Kanwisher, N. (1998). A cortical representation of the local visual environment. Department of Brain and Cognitive Sciences. Massachusetts Institute of Technology, Amherst Street, Cambridge, Massachusetts. Friston, K. Ashburner, J. Kiebel, S. Nichols, T. & Penny, W. (2011). Statistical parametric mapping: The analysis of functional brain images. London: Academic Press. Kanwisher, N., McDermott, J., Chun, M. (1997). The fusiform face area: A module in human extrastriate cortex specialized for face perception. The Journal of Neuroscience, 17(11): 4302–4311 Miller, B. & Cummings, J. (2007). The human frontal lobes: functions and disorders. New York and London: The Guilford Press. Park, S. & Chun, M. (2009). Different roles of the parahippocampal place area (PPA) and retrosplenial cortex (RSC) in panoramic scene perception. NeuroImage, 47: 1747–1756. Pearlman, A., Birch, J., & Meadows, J. (1979) Cerebral color blindness: an acquired defect in hue discrimination. Ann Neurol 5:253–261. Schacter, D., Gilbert, D. & Wegner, D. (2011). Psychology. New York, NY, USA: Worth Publishers. Sergent, J. & Signoret, J.L. (1992). Functional and anatomical decomposition of face processing: evidence from prosopagnosia and PET study of normal subject. The Royal Society, 335: 55–62 Watson, J., Myers, R., Frackowiak, R., Hajnal, J. V., Woods, R. P., Mazziotta, J. & Zeki, S. (1993). Area V5 of the human brain: evidence from a combined study using positron emission tomography and magnetic resonance imaging. Cerebral Cortex, 3(2): 79-94. Zeki, S., Watson, D., Lueck, C. & Friston, K. (1991). A direct demonstration of functional specialization in human visual cortex. The Journal of Neuroscience, 17(3): 641-649 Zihl, J, von Cramon, D., & Mai, N. (1983) Selective disturbance of movement vision after bilateral brain damage. Brain, 106(3): 13-340. Zysett, S. Huber, O., Samson, A., & Ferts E. (2003). Functional specialization within the anterior medial prefrontal cortex: a functional magnetic resonance imaging study with human subjects. Neuroscience Letters, 335: 183–186. Read More