Transcript plastic
Origin of Mind Chapter 4 Evolution and Development of Brain and Cognition pp.85-124 Is the Human Mind Unique? It is unique in its advanced level of development, but not in the process by which it achieved this development. The human mind is a product of the activity of the brain, and the human brain (like any other brain) is a product of evolutionary selection pressures. Selection pressures have produced not only the innate instincts of simpler animals, but also the most highly advanced forms of human cognition. Continuum of Brain Plasticity CONSTRAINED more specific governed by genes inherited from ancestors Better suited for addressing invariant features of the environment PLASTIC more adaptable governed by experience developed over time Better suited for addressing variant features of the environment Inheriting the Brain: The Tree of Life Inheriting the Brain: Homologous Structures A homologous characteristic is a trait that appears in two or more organisms due to their sharing a common ancestor. Inheriting the Brain: Homologous Structures Humans share many homologous brain structures and attributes with other mammals. This includes the appearance of the neocortex, which is the newest and outermost layer of the cerebral cortex. - Thalamus a. Superior colliculi b. Inferior colliculi - Hypothalamus - Hippocampus - Neocortical regions a. Auditory b. Visual c. Somatosensory Inheriting the Brain: Neocortical Regions p.91 Inheriting the Brain: Genes Humans also share certain homologous genes with other mammals (and even non-mammal species) that control key aspects of the prenatal development of the brain. However: a. Humans have a greater number of genes that are devoted to brain development. b. Some homologous genes may be expressed differently in different species. Inheriting the Brain: Two Models of Neocortical Development Arealization – formation of the functional subdivisions of the neocortex (e.g. visual cortex) during prenatal development. 1. Intrinsic Model: Arealization is a result of the characteristics of the neocortex itself. Protomap hypothesis: The neocortex differentiates automatically during its development, according to genetic controls. 2. Extrinsic Model: Arealization is a result of thalamic inputs. Protocortex hypothesis: The neocortex is undifferentiated until the thalamus directs particular neural signals (e.g. auditory) to a particular neocortical area, causing subdivisions to form. Inheriting the Brain: Comparative Ecology Comparative ecology – the study of variations in the ecological niche of different species. When we compare species that are closely related (having a recent common ancestor) but have adopted different survival strategies, we can observe alterations in brain organization that are not likely the result of long-term evolutionary changes. When a body part becomes more specialized for obtaining food, the corresponding area of the somatosensory cortex (which contains a sensory “map” of the body) can become enlarged. This is called cortical magnification (see next slide). Inheriting the Brain: Comparative Ecology p.100 Molding the Brain: How Experience Shapes The Mind While it is certain that selection pressures allowed us to develop brains in the first place, selection pressures are not necessarily responsible for the specialization of all brain areas. Most notably, if the neocortex were to expand for reasons other than selection pressures, the resulting unspecialized neocortical areas could make the brain highly plastic. If so, the plasticized brain could be profoundly “molded” by incoming stimuli. Molding the Brain: Allometric Expansion Allometry - systematic relations among different features of the body. 1. There is an allometric relation between body size and brain size: they tend to roughly maintain their ratio. It is conceivable that an increase in body size (perhaps due to climatic pressures) caused an incidental allometric expansion of the brain. However, the body-brain size relationship is unreliable. 2. Finlay and Darlington (1995) – based on an analysis of the sizes of 12 brain regions in 131 species, they proposed that a neocortical expansion due to genetic changes affecting progenitor cell division had resulted in an incidental allometric expansion of other brain areas. Molding the Brain: Allometric Expansion cont'd. ...However, other researchers have analyzed the same data set as Finlay and Darlington (1995) and have drawn a different conclusion: that ecological and social adaptations, not allometric expansion, caused the increases in neocortical volume. This conclusion was further solidified by a comparison of the brain proportions of New and Old World monkeys. These geographically separated but socially similar groups demonstrated convergent evolution of their brain proportions. Molding the Brain: Injury and Learning Brain injury, or the amputation of a body part, can result in subsequent reorganization of disrupted cortical functioning. Learning, particularly rehearsal (repetitive actions) can lead to changes in cortical functioning. Similarly, stimulation with or deprivation of certain stimuli can alter the behavior of the cortex. Functional adaptations due to injury and learning are examples of plasticity. Soft Modularity Refer to TABLE 4.1 on p.114, and TABLE 4.2 on p.117 for a complete explanation of the types of modules and plasticity.