Neuroscience and Behavior
KEY POINTS
Introduction: Neuroscience and Behavior
Psychological and biological processes are closely linked. Biological psychologists investigate the physical processes that underlie psychological experience and behavior. Neuroscience is the study of the nervous system, especially the brain.
The Neuron: The Basic Unit of Communication
Information in the nervous system is transmitted via cells specialized for communication, called neurons. There are three basic types of neurons: sensory neurons, motor neurons, and interneurons.
Most neurons have three basic components: a cell body, dendrites, and an axon.
Glial cells help neurons by providing structural support, removing waste products, and producing the myelin sheath, which helps insulate one axon from other axons. Glia are also involved in brain development and the communication of information between neurons.
Within the neuron, information is communicated in the form of brief electrical messages called action potentials. The minimum level of stimulation required to activate a neuron is called the stimulus threshold. A neuron’s resting potential is the state in which it is ready to activate and communicate its message if sufficiently stimulated. According to the all-or-none law, either a neuron is sufficiently stimulated and an action potential results, or it isn’t sufficiently stimulated and an action potential doesn’t occur.
The point of communication between two neurons is called the synapse. Neurons communicate information to other neurons either electrically or chemically. In chemical communication, neurotransmitters cross the synaptic gap and affect neighboring neurons. These neurotransmitters are held within synaptic vesicles, which float in axon terminals. The entire process of transmitting information at the synapse is called synaptic transmission. Reuptake is the process in which neurotransmitter molecules detach from the receptor and are reabsorbed and recycled.
There are many different kinds of neurotransmitters, which send either excitatory or inhibitory messages to the receiving neuron. Some drugs influence behavior and mental processes by influencing neurotransmitter activity. Important neurotransmitters include acetylcholine, dopamine, serotonin, norepinephrine, GABA, glutamate, and endorphins.
Drugs can mimic specific neurotransmitters. An agonist is a drug or other chemical that binds to a receptor. A drug can also act as an antagonist by blocking the effect of neurotransmitters.
The Nervous System and the Endocrine System: Communication Throughout the Body
The nervous system is divided into two main divisions: the central nervous system (CNS) and the peripheral nervous system. The central nervous system is composed of the brain and the spinal cord. The spinal cord can produce spinal reflexes.
The peripheral nervous system consists of all the nerves outside the central nervous system. The two main subdivisions of the peripheral nervous system are the somatic nervous system and the autonomic nervous system. The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system.
The endocrine system is composed of glands that secrete hormones into the bloodstream, regulating many body functions, including physical growth, stress response, and sexual development. The endocrine system itself is regulated by the hypothalamus in the brain. Under the direction of the hypothalamus, the pituitary gland directly controls hormone production in other endocrine glands as well as hormones that act on physical processes. Oxytocin is a hormone involved in reproduction, social motivation, and social behavior. Another set of glands, called the adrenal glands, which include the adrenal cortex and the adrenal medulla, produce hormones that are involved in the human stress response. The gonads are endocrine glands that secrete hormones that regulate sexual characteristics and reproductive processes.
A Guided Tour of the Brain
Most psychological processes involve the integrated processing of information via neural pathways in multiple brain structures and regions.
The human brain can change in response to environmental stimulation, training, or experience, displaying both functional plasticity and structural plasticity.
Evidence suggests that neurogenesis, the development of new neurons, can occur in the adult brain.
The major regions of the brain are the hindbrain, the midbrain, and the forebrain. Combined, the hindbrain and midbrain structures constitute the brainstem. Sensory and motor pathways cross over in the hindbrain. The key structures of the hindbrain are the medulla, the cerebellum, and the pons. The reticular formation is located in the core of the medulla and the pons.
Auditory and visual information is integrated and coordinated in the midbrain. The substantia nigra is involved in motor control and contains a concentration of neurons that produce dopamine.
The outer portion of the forebrain is called the cerebral cortex. The cerebral cortex is divided into the left and right cerebral hemispheres, with the corpus callosum serving as the main communication link between them. Each hemisphere is divided into four lobes. The temporal lobe contains the primary auditory cortex. The occipital lobe contains the primary visual cortex. The parietal lobe contains the somatosensory cortex. The frontal lobe contains the primary motor cortex. The remainder of the cerebral cortex is composed of association areas.
The limbic system structures are found beneath the cerebral cortex and form neural circuits that play critical roles in learning, memory, and emotional control. The limbic system includes part of the frontal cortex and the hippocampus, thalamus, hypothalamus, and amygdala.
Specialization in the Cerebral Hemispheres
The notion that particular areas of the brain are associated with particular functions is called cortical localization. In the mid-1800s, it was discovered that damage to the left hemisphere produced disruptions in speech and language called aphasia. Different forms of aphasia include Broca’s aphasia and Wernicke’s aphasia. Damage to the same areas of the right hemisphere did not produce aphasia. The notion that specific psychological or cognitive functions are processed primarily on one side of the brain is called lateralization of function.
More evidence for the specialized abilities of the two hemispheres has resulted from the split-brain operation, in which the corpus callosum connecting the two hemispheres is cut. Roger Sperry and his colleagues demonstrated the different strengths of each hemisphere in split-brain patients. The left hemisphere is specialized for language tasks, and the right hemisphere is specialized for visual-spatial tasks.
Match each of the terms on the left with its definition on the right. Click on the term first and then click on the matching definition. As you match them correctly they will move to the bottom of the activity.
Pierre Paul Broca (1824-1880) French surgeon and neuroanatomist who in 1861 discovered an area on the lower left frontal lobe of the cerebral cortex that, when damaged, produces speech disturbances but no loss of comprehension. (p. 73)
Roger Sperry (1913-1994) U.S. psychologist who received the Nobel prize in 1981 for his pioneering research on brain specialization in split-brain patients. (p. 75)
Karl Wernicke (1848-1905) German neurologist who in 1874 discovered an area on the left temporal lobe of the cerebral cortex that, when damaged, produces meaningless or nonsensical speech and difficulties in verbal or written comprehension. (p. 73)