The cortex, which is the outermost and latest development in the evolution of the vertebrate brain, is believed to be the central site of consciousness and intelligence, performing the most complex associative and mnemonic functions. The gray matter (the fissured and convoluted outer surface) is largely composed of neuron cell bodies stacked approximately 3 mm thick. Underlying the cortex is a white medullary structure composed of myelinated axonal fibers that communicate with different parts of the cortex and other proximal and distal areas of the brain. Beneath the medullary white matter are the basal ganglia, a collection of subcortical nuclei involved in the mediation of complex movement, like walking and running. Removal of the cerebral cortex (but sparing the basal ganglia) results in the loss of sophisticated locomotor skills, but other motor activities, like running, walking, fighting, and sexual behavior, are not significantly affected. Besides motor functions, the cerebral cortex is intimately involved in the organization of somatosensory information and the elaboration of various cognitive functions, like learning and problem solving.
The cerebral cortex is divided into two large left and right hemispheres that are interconnected by the corpus callosum and other commissure fiber bundles, allowing the two sides of the brain to communicate with each other. An interesting feature of the cerebral cortex is that its two sides have a contralateral relationship with the body—for example, impulses originating on the right side of the cortex are responsible for motor activity on the left side of the body and vice versa. The cortex is functionally sectioned into several areas serving distinct roles: the frontal lobe (serving various unifying and associative functions), the temporal lobe or auditory cortex (responsible for receiving and processing auditory information), the precentral lobe or primary motor cortex (involved in fine motor activity), the parietal lobe (receiving somatic-tactual sensory input from the skin and body), and the occipital lobe (receiving and processing visual inputs).
The prefrontal cortex located in the frontal lobe receives input from many parts of the brain and assesses it in terms of a dog's changing needs, goals, and the current demands of the internal and external environment. in addition to the assessment of input, the prefrontal cortex decides on the course of action needed and directs the expression of programmed species-typical action patterns. The prefrontal cortex evaluates the effect of such behavior via reward-punishment outcomes (Suvorov et al., 1997). Consequently, pathways originating in the prefrontal cortex appear to play a very significant role in the coordination of goal-directed behavior, perhaps in conjunction with the behavioral activating system as previously described. Damage to the prefrontal cortex produces a number of significant cognitive and emotional dysfunctions. Allen and colleagues (1974) found that dogs that had undergone prefrontal lobotomy exhibited a high degree of distractibility, but, paradoxically, once they managed to focus on something, they seemed to hold their attention on it for an unusual length of time. Emotionally, the dogs with prefrontal damage (especially involving the or-bitofrontal area) appeared disorganized and uninhibited. For example, the authors mention one dog that "growled while experiencing seemingly pleasurable stimuli" (1974:207).
The frontal cortex is a unifying association structure, serving many cognitive, memory, emotional, and motor functions. The pre-frontal lobes appear to play a prominent role in learning, especially learning that requires a mental representation of the world. Animals suffering lesions to this area of the brain can learn simple conditioned associations and perform appropriate instrumental responses as long as the necessary information required to learn the behavior and perform it are present and held constant (e.g., a discrimination task involving a positive and a negative stimulus). However, animals with prefrontal lesions do poorly when required to perform a delayed-response task. For example, if a pre-frontally damaged dog is shown the location of a piece of food and then briefly removed from the room, the dog would display a much retarded ability to remember where the item was last seen a few moments before. Mastering a delayed-response task requires that dogs form a mental picture or representation of the context and the location of the item in that context. Such effects of lesioning suggest that the frontal cortex plays an important role (in conjunction with limbic structures like the hippocampus and amygdala) in the operation of working memory (Goldman-Rakic, 1992).
The temporal cortex, which is located laterally on the cortex toward the front, is primarily concerned with the organization of information derived from audition. Cortical functions originating in the temporal lobes also appear to play an important role in the formation of complex visual patterns. A dog's ability to recognize its owner's face from others probably involves the participation of the temporal lobe. This area is the only cortical structure to receive projections from all the sensory modalities. The temporal lobes play an important role in the higher elaboration and the conscious experience of emotion, receiving projections from the limbic system and more primitive input directly from the thalamus. Monkeys that have undergone extensive damage to the temporal lobes do not exhibit normal fears and anxieties, are unusually calm and placid while being handled, and tend to engage in compulsive oral behavior. For instance, unlike normal monkeys, le-sioned animals may pick up snakes and lighted matches without exhibiting any apparent fear. These effects of temporal lobe le-sioning and damage to underlying limbic structures located in the temporal lobes are collectively referred to as the Kluver-Bucy syndrome (Kluver and Bucy, 1937). The authors refer to these phenomena as examples of "psychic blindness," arguing that the absence of fear could not be fully explained by reduced emotional reactivity alone, suggesting that the lesioned animals may simply fail to "recognize" the items as innately feared objects.
Considering the important associative and regulatory functions that are performed by the frontal cortex, it would seem reasonable to conclude that the frontal cortex (especially localized in the prefrontal and orbitofrontal areas) probably plays a considerable role in the control of impulsive and episodic behavior, such as aggression and panic. In addition to exercising regulatory control over target subcortical trigger sites (e.g., the amygdala and hypothalamus) and motor programs in the basal ganglia, it is a central area for interpreting and integrating the hedonic arousal resulting from highly motivated behavior, thereby providing a means to enhance central control over such impulses through learning. Unfortunately, as noted by LeDoux (1996), the connections from the amygdala to the cortex are far stronger than the regulatory connections from the cortex to the amyg-dala—a functional asymmetry that may help explain the failure of some animals to gain full control over their fearful or aggressive impulses (Fig. 3.4). Also, some evidence suggests that the prefrontal cortex is affected by the dimorphizing influence of perinatal hormones (Kelly, 1991), perhaps affecting cortical regulatory control over fear and aggression, as well as influencing many other neural activities. This possibility is consistent with the general observation of trainers and behav-iorists that male dogs present more frequently with aggression and other common behavior problems than female dogs. Although various mechanisms and neural sites are probably influenced by such hormonal activity, the pre-frontal area may be particularly important because of the influence that it appears to exert on the perception of social signals and the
Cognition Emotion PNS/SNS Activity
Fig. 3.4. Diagram of the asymmetrical interactions between cortical, subcortical, and autonomic neural processes. PNS, parasympathetic nervous system; SNS, sympathetic nervous system.
coordinated actions that it directs in response to that information. Brain and Haug describe the close relation between hormones and social communication:
Hormones can be regarded as acting on situa-tional factors by altering the perception of signalling between conspecifics. Evidence for hormonal involvement in perception has been obtained for all the major sensory systems. ... Hormones also may alter the probability of the production of signals that serve social functions. The most frequently modified signals are somatosensory, olfactory, visual, and auditory. For example, androgens and estrogens have major effects on olfactory social communications in both rodents and infra-human primates. (1992:543-544)
The parietal lobes, which are located on either side of the cortex toward the rear, make up a central cortical region mainly involved with processing somatosensory information from the body. This area is concerned with the senses of touch (pressure), warmth, cold, and pain. It is also responsive to propri-oceptive sensory input from the muscles, tendons, and joints. The parietal area contains several mental representations of the body mapped out over its surface that correspond to various parts of the body. Depending on the amount of sensory input and the particular sensory modality's importance to the species involved, the size of any particular area represented in the cortex will vary. Rats (which depend on their whiskers to a great extent) have a disproportionately large area of their somatosensory cortex devoted to the mapping and representation of sensory input from their whiskers. Eichelman (1992) has noted that the mere clipping of a rat's whiskers has an equivalent suppressive effect on affective aggression as a bilateral amyg-dalectomy. The amount of the cortex mapped for any sensory modality is proportionately correlated with the relative size of the thalamic relay involved (Thompson, 1993). The occipital lobe is located at the rear of the brain and is primarily involved in the processing of visual information relayed to it by the thalamus. Extensive lesioning of the occipital lobe of the cerebral cortex results in blindness.
Even though a dog's behavior is strongly influenced by intrinsic neurobiological processes, it remains flexible and responsive to the adaptive influence of learning. An important function of behavioral intervention is to improve a dog's ability to focus attention, to exercise impulse control, and to develop a more adaptive repertoire of coping strategies. Most veterinary clinicians emphasize the importance of adjunctive behavior modification when administering psychotropic medications, such as fluoxetine. While the subcortical circuits mediating the expression of affective aggression can be modulated by such drugs, treatment is only lastingly effective if corresponding cortical regulatory control is enhanced at the same time through learning. In severe cases, medications may help dogs to obtain better self-control over their dysfunctional or problematic impulses, but such drugs can never take the place of sound training and behavioral intervention.
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