A young Canadian woman who was admitted to the hospital with a stroke completely lost the hunger for a year. The experts who examined her believe that the cause of such an unusual symptom is damage to the left insular lobe.
As noted in an article for the journal Neurocase, this case highlights the important role of the insular lobe in taste perception and appetite control.
With a stroke, blood circulation in the brain is severely disrupted, which can lead to damage to its individual parts. As a result, the functions associated with them suffer. For example, damage to the frontal and temporal lobes of the left hemisphere causes speech impairments. In addition, stroke often causes paralysis of the limbs or the entire body.
A team led by Dang Khoa Nguyen of the University of Montreal described a very unusual case of the consequences of a stroke. Their focus was on a twenty-eight-year-old Canadian woman who was in her second month of pregnancy (and had given birth to twins seven months earlier). The woman was admitted to the hospital with paralysis of the right side of her body and obvious speech impairments. Using MRI, doctors diagnosed an acute ischemic stroke of the left insular lobe (the part of the cerebral cortex located deep in the lateral sulcus).
Eleven days later, the patient recovered, so she was discharged from the hospital. After discharge, the woman took acetylsalicylic acid as the only treatment. Over the course of several months, her condition gradually improved, but she continued to feel weak. In addition, the patient found that in the six months after the stroke, she had never experienced a feeling of hunger, which caused her to inadvertently skip meals. Initially, the woman attributed this symptom to fatigue, but it persisted even after her condition improved.
Seven months after hospitalization, the patient was examined by specialists from the University of Montreal. They found that even with a lack of calories, the woman did not feel any physiological signals that it was time for her to eat, for example, a rumbling in her stomach. Despite the fact that the patient did not have problems with the sense of taste, smell and texture of food (only in the first two months she complained of a metallic aftertaste after eating any food), even her favorite foods and products, for example, chocolate. The woman did not experience other psychological problems, such as anhedonia or bad mood.
When, sixteen months after the stroke, the patient came for a second examination, she reported that about a month before, the feeling of hunger had returned to her. In total, the unusual symptom lasted for about a year. During this time, the woman lost about ten kilograms: if at the time of the stroke her weight was about 73 kilograms, then sixteen months later it dropped to 60 kilograms. The patient did not follow any special diets, and also did not use psychoactive substances – but due to the disappearance of her appetite, she ate half as much as usual. Given that the survey did not reveal any signs of eating disorders, the researchers linked the problem to the effects of a stroke.
As noted by Nguyen and his colleagues, this is the first case of loss of hunger due to ischemic stroke described in the literature. In their opinion, the cause of the symptom was damage to the left insular lobe – a part of the brain that plays one of the most important roles in processing taste signals, and also participates in the control of appetite and energy balance. In particular, the insular lobe helps to assess the physiological state of the body.
It is assumed that the insular lobe integrates information about taste and body sensations, which allows making decisions about food intake at a higher level. Moreover, the functions of this region of the brain seem to be asymmetric: the left insular lobe is associated with the parasympathetic nervous system, and the right one with the sympathetic.
If this idea is correct, then damage to the left insular lobe in a Canadian patient led to an imbalance in the autonomic nervous system and increased sympathetic function, which in turn reduced food intake.
In addition, damage to the parasympathetic nerve pathways associated with the left insular cortex could adversely affect the ability to perceive hunger.
Interestingly, patients whose islet lobe was damaged as a result of surgery (e.g., in the surgical treatment of epilepsy) also reported a change in appetite and perception of taste.
Surgical removal of some parts of the brain sometimes leads to unexpected consequences: for example, without one of the amygdala, a person may stop feeling fear, and without the frontal lobes – get rid of apathy, but acquire problems with memory, speech and decision-making.
Image Credit: GEtty