Kluver-Bucy syndrome is a very rare behavioral disorder triggered by damage to both temporal lobes of the brain.
This paragraph shall merely serve as an orientation for symptoms that may be experienced by KBS patients. As has been mentioned before, humans typically do not present all of them at once .
KBS may be associated with emotional changes, particularly with placidity and affective indifference. Patients may even be apathetic and may not react accordingly to external stimuli. Facial expressions, gestures and speech are dull. This emotional emptiness becomes most clear when these patients are exposed to fear-triggering objects and situations. In some cases, fear may, however, be expressed in non-dangerous situations.
The term hyperorality is often used in relation with KBS and describes an excess need to explore one's surroundings with the mouth . Such behavior may not only be harmful, but is socially not accepted. KBS patients may suddenly start to lick objects in public. Some patients present a general, enhanced urge to explore with any sense available. This may be as much of a social problem as the aforementioned oral tendencies since people in public are not welcome to touch anything in view.
There may be a relation between these oral tendencies and dietary changes. Affected individuals eat in excess, they may place anything edible and non-edible into their mouth. The former will lead to obesity in the short run; the latter may cause life-threatening damage to the gastrointestinal tract or may lead to intoxication.
Visual agnosia may either occur due to failures in physiological processing of sensory inputs or because of the inability to associate objects viewed with pre-existing memories. Thus, the eyes of KBS patients may see an object, but the respective information may never be assembled or connected with memories. Visual agnosia enhances hyperorality.
Memory loss is experienced in some cases.
The increased sexual urge associated with KBS may be a major problem for affected people. They may engage in overt, public sexual behavior and criminally relevant activities such as uninvited attempts to have sex .
KBS as a behavioral disorder may be diagnosed based an the patient's medical history and clinical examination. It may, however, be very challenging to diagnose the underlying disease . Symptoms not characteristic for KBS may be of great value to this end.
Depending on the list of most likely differential diagnoses, distinct measures need to be taken. Herpes simplex encephalitis is often associated with headaches and fever and may be diagnosed after analyzing a sample of liquor cerebrospinalis. Imaging diagnostics may be the approach of choice to identify several of alternative, less frequent causes of KBS. Magnetic resonance imaging and computed tomography scans of the brain may reveal signs of inflammation, ischemia, neoplasms and other pathologies. An electroencephalogram may be helpful in identifying the cause of seizures.
In general, patients need to be monitored to prevent they harm themselves, e.g., by ingesting non-edible objects. Dietary controls are required to avoid bulimia, subsequent overweight and obesity. Inappropriate, public behavior should be evaded. There is at least one case report where such behavior lead to criminal conviction .
Additionally, an adequate treatment of the underlying disease is required. In case of herpes simplex encephalitis it mainly consists in prolonged application of anti-viral drugs. Drug resistances might be encountered and indicate administration of another compound. Even after successful treatment of herpes simplex encephalitis, relapses may occur and manifest in form of sudden behavioral changes. In these patients, the anti-viral therapy needs to be re-initiated as soon as possible . Other primary disease require distinct therapeutic approaches.
Prognosis varies largely . It improves significantly if the underlying disease can be treated. In this context, more effective anti-viral medication may change the average outcome of herpes simplex encephalitis. This may be associated with less mortality of the latter, an higher incidence of KBS, but a better prognosis for patients that do develop this behavioral disorder.
As has been indicated in the previous paragraph, temporal lobes and amygdalas fulfill a variety of tasks regarding processing and association of visual and auditory input, memory and emotions. Distinct parts of the aforementioned brain structures may account for all these functions. Complete malfunction would thus require extensive lesions that comprise large parts of the temporal lobes and amygdalas, and this situation is rarely given in humans. However, partial injury may trigger some of the symptoms traditionally associated with KBS.
This "partial injury" may result from different cerebral disorders such as inflammation due to infections or autoimmune responses, vascular diseases, traumas, metabolic disorders, neoplasms and neurodegeneration: The most common trigger for KBS is an infection with the herpes simplex virus that lead to herpes simplex encephalitis. Tuberculosis may also be associated with KBS . Cerebral infarction may occur in this part of the brain and cause functional impairment of the temporal lobes. Any other condition involving cerebral ischemia, hypoxia and hypoglycemia may have similar consequences as a stroke. Traumatic insults are another possible cause of KBS , although these most frequently involve injury to other cerebral areas. Of note, trauma may be understood in the broader sense of the word and does also include tissue damage or resection during surgical interventions. Niemann-Pick disease and porphyria may serve as examples for metabolic disorders triggering KBS. The disease has been described in relation with Alzheimer disease . Neuronal ceroid lipofuscinosis is another neurodegenerative disease possible associated with KBS; it may affect children and adolescents.
KBS is a very rare disease. A literature review reveals several descriptions of isolated cases but no larger studies on the disease. It is tempting to speculate that the age distribution of KBS reflects that of its underlying diseases, but this hypothesis has not yet been confirmed. KBS can occur at any age. It has been described in children . Men and women are equally affected.
The main functions of the temporal lobe are processing of visual and auditory sensory inputs, associating this input with pre-existing memories and connecting it with an emotional component, and creating new, long-term memory. For instance, the healthy rhesus monkeys used by Klüver and Bucy reacted with fear to snakes, i.e., they saw the snake, possibly associated this visual input with a previous, unpleasant memory or just reacted on instinct and labeled the corresponding object as dangerous. This chain of events was not any longer present in rhesus monkeys that underwent bilateral lobectomy. They remained placid, possibly even interested in front of the snake.
Lobectomies may be required in humans after severe accidents, due to epilepsy or neoplasms, but most KBS patients suffer from partial temporal lobe damage. The above mentioned functions are fulfilled by neurons located in different layers of the temporal lobe and depending on the precise site of lesion, some KBS symptoms will be developed and others will not. Presentation of three typical symptoms is considered diagnostic for KBS and in humans, most frequently manifested symptoms are affective indifference and a tendency to explore one's surroundings with the mouth. The latter may be related with an abnormally high demand for comestibles. Impaired association of sensory input with pre-existing memories may show in form of the inability to recognize objects and persons.
The early diagnosis of primary diseases may allow for therapy in a timely manner and may thus diminish lesions to the temporal lobes and amygdalas. Herpes simplex encephalitis, for instance, may easily be misdiagnosed .
Heinrich Klüver and Paul Bucy were both neuroscientists that practiced in the United States during the first half of the 20th century. They worked with rhesus monkeys and conducted experiments in order to shed light on the function of their temporal lobes. In this context, they described behavioral changes that resulted from bilateral lesion of the temporal lobes of these animals and designated the whole of these symptoms as Kluver-Bucy syndrome (KBS) . In detail, they observed the following:
Today, the function of the temporal lobe is known in much more detail. For instance, this part of the brain is involved in visual processing. Visual agnosia may thus be perfectly explained by temporal lobe lesions.
The amygdala is located within the medial part of the temporal lobe and fulfills important functions in emotional assessment and association. Here, sensory impressions may be evaluated as stemming from a possibly dangerous object and protective fear is generated. Therefore, if temporal lobe injury involves the amygdala, the affective indifference previously observed in monkeys may develop. It has been proposed that the amygdala affects the sexual urge of a mammal.
In humans, a complete KBS is very rarely seen. Bilateral lesions of the temporal lobes that comprise the respective amygdalas may, however, be observed in patients suffering from systemic diseases associated with encephalitis. In practice, such patients almost exclusively suffer from herpes simplex encephalitis. Visual agnosia, affective indifference and, to a limited degree, an increased sexual urge are observed in humans. Patients also show signs of dementia, which may be ascribed to temporal lobe functions regarding memory. Seizures may be experienced. It has to be noted that the clinical presentation of these patients may be dominated by symptoms triggered by other, more severe neural lesions.
Kluver-Bucy syndrome (KBS) describes a behavioral disorder resulting from bilateral lesions to temporal lobe and amygdala. The latter are part of the cerebral cortex and fulfill a variety of functions comprising processing of visual and auditory sensory inputs, associating this input with pre-existing memories, connecting it with an emotional component, and creating new, long-term memory.
Any cerebral disorder causing damage to both temporal lobes and amygdalas may trigger KBS. The most common cause of this disease is an encephalitis due to infection with herpes simplex virus. But trauma, cerebral infarction, a neurodegenerative disease such as Alzheimer disease, certain metabolic disorders and brain tumors may also account for temporal lobe lesions and subsequent KBS.
Diagnosis is based on the medical history of the patient and the results of a clinical examination. Laboratory analyses of blood and cerebrospinal fluid as well as imaging diagnostics, mainly magnetic resonance imaging and computed tomography scans are applied to identify the cause of KBS. More specific examinations may follow depending on the results of the former.
If the underlying disease has been identified, it should be accordingly treated. Prognosis of KBS improves significantly if the primary disorder can be cured.