Sensory and Motor Cortex
65 The Central Nervous System: Making Sense of the World Cerebral cortex Functional areas Anatomical areas Frontal lobe FIGURE Temporal lobe Parietal lobe Occipital lobe Association cortex Motor cortex Somatosensory cortex Association cortex Broca’s area Auditory cortex Wernicke’s area Visual cortex 2.10 The Cerebral Cortex (viewed from the left side) The brain’s ridges (gyri) and valleys (sulci) are landmarks that divide the cortex into four lobes: the frontal, parietal, occipital, and temporal. These terms describe where the regions are (the lobes are named for the skull bones that cover them), but the cortex is also divided in terms of function. These functional areas include the motor cortex (which controls movement), sensory cortex (which receives information from various senses), and association cortex (which integrates information). Also labeled are Wernicke’s area and Broca’s area, two regions that are found only on the left side of the cortex and that are vital to the interpretation and production of speech (Peña et al., 2003). sensory cortex The part of the cerebral cortex located in the parietal, occipital, and temporal lobes that receives stimulus information from the skin, eyes, and ears, respectively. The folds of the cerebral cortex give the surface of the human brain its wrinkled appearance, its ridges and valleys. The ridges are called gyri (pronounced “ji-rye”), and the valleys are known as sulci (pronounced “sulk-eye”) or ﬁssures. As you can see in Figure 2.10, several deep sulci divide the cortex into four areas: the frontal (front), parietal (top), occipital (back), and temporal (side) lobes. The gyri and sulci provide landmarks for describing the structure of the cortex, but the functions of the cortex do not follow these boundaries. When divided according to function, the cortex includes areas of sensory cortex, motor cortex, and association cortex. (“In Review: Organization of the Brain” summarizes the major structures and functions of the brain.) Sensory and Motor Cortex The sensory cortex lies in the parietal, occipital, and temporal lobes. Different regions of the sensory cortex receive information from different senses. Occipital lobe cells called the visual cortex receive visual information. Temporal lobe cells called the auditory cortex receive information from the ears. And information from the skin, such as touch, pain, and temperature, is received by cells in the parietal lobe. These skinrelated areas are called the somatosensory cortex (soma is Greek for “body”). Information about skin sensations from neighboring parts of the body comes to neighboring parts of the somatosensory cortex. It is as if the outline of a tiny person, dangling upside down, determined the location of the information (see Figure 2.11). This pattern is called the homunculus (Latin for “little man”). The amount of sensory cortex that responds to particular sensory stimulation can be modiﬁed by experience (Candia et al., 2003). For example, if a limb is lost, sensory cortex that had been stimulated by that limb will now be stimulated by other regions of skin. Similarly, practicing the violin will increase the number of sensory neurons that respond to touch; the same thing happens when blind people learn to read Braille with their ﬁngertips (Amedi et al., 2005; Pascual-Leone & Torres, 1993). 66 in review Chapter 2 Biology and Behavior ORGANIZ ATION OF THE BR AIN Major Division Some Major Structures Some Major Functions Hindbrain Medulla Regulates breathing, heart rate, and blood pressure Reticular formation (also extends into midbrain) Regulates arousal and attention Cerebellum Controls ﬁnely coordinated movements and certain cognitive processes Midbrain Various nuclei Relays sensory signals to forebrain; creates automatic responses to certain stimuli; initiates smooth movement Forebrain Thalamus Interprets and relays sensory information Hypothalamus Regulates hunger, thirst, and sex drives Amygdala Connects sensations and emotions Hippocampus Forms new memories Cerebral cortex Analyzes sensory information; controls voluntary movements, abstract thinking, and other complex cognitive activity Corpus callosum Transfers information between the two cerebral hemispheres ? 1. The oldest part of the brain is the . 2. Cells that operate as the body’s twenty-four-hour “time clock” are found in the . 3. Memory problems seen in Alzheimer’s disease are related to shrinkage of the . motor cortex The part of the cerebral cortex that controls voluntary movement. In the frontal lobe, speciﬁc neurons of the motor cortex control voluntary movements in speciﬁc parts of the body (Indovina & Sanes, 2001). The motor cortex’s arrangement mirrors that of the somatosensory cortex. So the parts of the motor cortex that control hand movement are near parts of the sensory cortex that receive sensory information from the hands. Seems easy, doesn’t it? You have a map of your body parts in your cerebral cortex, and you activate cells in the hand region of the cortex if you want to move your hand.