Impulsivity is a trend that can be found in the expression of different behaviors. In human medicine, impulsivity is commonly linked to disorders such as impulsive aggression, pyromania, pathological gambling, and sexual impulsions (Hollander, 2000). In veterinary medicine, impulsivity is commonly referred to aggressive behavior and can be defined as a reduction or a complete lack of warning signals previous to attack. The impulsive dog typically bites without the normal signs of aggression such as growls or bared teeth.
Impulsivity is more a sign than a diagnosis itself. In fact, impulsivity can be found as a component of the aggressive sequence of common canine aggression problems. From a clinical point of view, the manifestation of impulsivity can be very challenging to the clinician for three different reasons: first, it makes diagnosis more difficult; second, it is an element of bad prognosis; and third, it complicates treatment.
Aggression in dogs can be related to an underlying pathophysiological condition (Beaver, 1997). After medical problems have been ruled out, the cause of the aggressive behavior must be identified. Dogs can show aggression for different reasons. The number of diagnoses ranges from two to 20, depending on the author (Beaver, 1999). Common forms of aggressive behavior include dominance, fear, and interdog aggression. The individual causes of aggression can be identified only after careful history taking. The diagnostic protocol for canine aggression is based on three main characteristics: target of the attacks, contexts in which aggression occurs, and the dog’s posture before and during the aggressive episodes.
Except for predatory behavior, canine aggression has the main function of regulating the interspecific interactions between individuals both inside and outside the pack. To avoid severe fighting, canids use a complex ritualized visual and auditory communication system. In fact, a dog’s motivational state can be determined by the observation of its ears, tail, and face and body posture (Houpt, 1998). Two main postures can be found, offensive and defensive. The offensive posture includes rigid standing, ears and tail up, and a direct look. The defensive posture is somewhat opposite and is composed of flexed limbs, ears and tail down, and an indirect look. In overt aggression, both postures are accompanied by growls and bared teeth. Often, elements of these two postures can be seen in the same dog showing the existence of a motivational conflict.
Impulsivity can be considered a modification of the normal aggressive sequence. When impulsivity is present, dog’s body posture and warning signals may not be correctly identified. From this perspective, the expression of impulsivity could be considered abnormal. In fact, in human medicine, impulsivity is one of the findings that distinguished pathological from normal aggression (Conacher, 1997). When impulsivity appears, diagnosis must rely on the context in which aggression occurs. Occasionally, however, the dog can act impulsively in some occasions but not in others. The dog’s posture during non-impulsive aggressive episodes can help to identify the underlying motivation for the problem.
One of the elements of bad prognosis is the inability for the owner to predict when the dog is going to bite (Reisner, 1994). By nature, impulsivity impedes the anticipation of the attack. Consequently, there is no possibility to avoid biting if the dog is presented with the trigger stimulus. Sometimes, however, this is a consequence of the owner’s lack of knowledge about normal canine communication. In this situation subtle signals preceding biting are missed by the owners. This could be termed false impulsivity and emphasizes the need to educate owners about the canine communication system.
Addressing impulsivity starts with the treatment of the underlying aggressive behavior problem. Treatment of behavior problems usually combines behavior modification techniques with the use of psychotropic drugs. Behavior modification protocols differ according to the cause of aggression, for example, dominance or fear (Overall, 1997). As a part of the treatment protocol, owners are instructed to avoid situations that lead to aggression. When impulsivity is present, owners must be especially careful.
Even though the expression of aggression is a complex interaction between genetic and environmental factors (Seroczynski, 1999), impulsivity seems to be linked to the dysfunction of certain neurotransmitters. Serotonin plays a very important role in the neurochemical control of aggression, especially when a component of impulsivity is present. Research done in humans and animals demonstrates a relationship between low levels of serotonin and the rise of impulsivity (Lesch, 2000; Miczek, 1998; Stanley B, 2000). A recent study in dogs reveals low levels of 5-HIAA, a serotonin metabolite, in dominant aggressive dogs, especially in those that bite without warning signals (Reisner, 1996).
The understanding of the biochemical basis of impulsivity helps to establish the use of psychotropic drugs to treat the condition. Drugs more commonly recommended are those that regulate the serotonin turnover, more specifically the selective serotonin reuptake inhibitors (SSRI). Fluoxetine (1 mg/kg q24) is the drug most commonly prescribed by veterinary behaviorists (Overall, 1997; Dodman, 1998). The SSRI stabilize serotonin levels, which results in a reduction of impulsivity (Hollander, 2000). However, their effects are not immediate and can take several weeks to become clinically apparent.
Although serotonin is the molecule that has received more attention during the past decade, it should be noted that different neurotransmitter systems can overlap in the CNS. In fact, the involvement of serotonin in impulsivity has been linked to interactions with other neurotransmitters, especially dopamine (Coscina, 1997). Other drugs used in human medicine to control impulsive behavior are antipsychotics, lithium, and anticonvulsants. Most veterinary behaviorists use these drugs only to treat refractory cases of aggression, mainly due to their potential side effects (Overall, 1997; Dodman 1998).
Despite the evidence of the role of serotonin and other neurotransmitters in the manifestation of impulsive behavior, it should be remembered that a modification in the level of a certain neurotransmitter might be the cause as well as the effect of behavioral changes. Impulsivity and aggressive behavior have to be treated as complex behavior problems where both internal and external factors play an interactive role.
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