Abstract
Background: Two main models have been advanced to explain the asymmetries observed in the representation and processing of emotions. The first model, labeled “the right hemisphere hypothesis,” assumes a general dominance of the right hemisphere for all emotions, regardless of affective valence. The second model, named “the valence hypothesis,” assumes an opposite dominance of the left hemisphere for positive emotions and the right hemisphere for negative emotions. Patients with frontotemporal lobar degeneration (FTLD) could contribute to clarifying this issue, because disorders of emotional and social behavior are very common in FTLD and because atrophy, which affects the antero-ventral part of the frontal and temporal lobes, can be clearly asymmetric in the early stages of this disease.Objective: The main scope of the present review therefore consists of evaluating if results of investigations conducted on emotional and behavioral disorders of patients with right and left FTLD, support the “right hemisphere” or the “valence” hypothesis.Method: A thorough review of behavioral and emotional disorders in FTLD patients, found that 177 possible studies, but only 32 papers met the requested criteria for inclusion in our review.Results: Almost all (25 out of 26) studies were relevant with respect to the “right hemisphere hypothesis” and supported the assumption of a general dominance of the right hemisphere for emotional functions, whereas only one of the six investigations were relevant with respect to the “valence hypothesis” and were in part consistent with this hypothesis, though these are also open to interpretation in terms of the “right hemisphere” hypothesis.Conclusions: This study, therefore, clearly supports the model of a general dominance of the right hemisphere for all emotions, regardless of affective valence.
Highlights
Even if most authors acknowledge that important asymmetries exist in the representation and processing of emotions, the nature of these asymmetries remains controversial
Almost all (25 out of 26) studies were relevant with respect to the “right hemisphere hypothesis” and supported the assumption of a general dominance of the right hemisphere for emotional functions, whereas only one of the six investigations were relevant with respect to the “valence hypothesis” and were in part consistent with this hypothesis, though these are open to interpretation in terms of the “right hemisphere” hypothesis
The same authors investigated the relationship between comprehension of specific emotions and regional cerebral volumes and showed that both happiness and sadness measures were significantly correlated with the right amygdala and the right orbito-frontal cortex (OFC) volume
Summary
Even if most authors acknowledge that important asymmetries exist in the representation and processing of emotions, the nature of these asymmetries remains controversial. The first model, labeled “the right hemisphere hypothesis” (Gainotti, 1972, 2012; Borod et al, 1998; Mandal and Ambady, 2004), posits a general dominance of the right hemisphere for all emotions, regardless of affective valence This model was proposed by Gainotti (1972) on the basis of clinical observations made in patients with right and left hemisphere lesions, because (aphasic) left braindamaged patients typically showed “catastrophic reactions” in their frustrating attempts of verbal expression, whereas patients with severe right hemisphere lesions typically showed an “indifference reaction” in their defects and disabilities. Patients with frontotemporal lobar degeneration (FTLD) could contribute to clarifying this issue, because disorders of emotional and social behavior are very common in FTLD and because atrophy, which affects the antero-ventral part of the frontal and temporal lobes, can be clearly asymmetric in the early stages of this disease
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