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Thou Shalt Not Kill: Moral Reasoning in Frontotemporal Dementia

This article explores the plausible neurobiological basis for deviations in moral reasoning in individuals with frontotemporal dementia by reviewing and summarizing a paper by Strikwerda-Brown and others (2021) published in the journal 'Brain'.


In any functional society, moral reasoning is the cornerstone of cooperative social behaviour. When it comes to studying moral decision making, researchers often take one of two routes– they either examine how moral reasoning develops during early years or how it changes with aging. While developmental studies look into the origins and development of the capacity for moral reasoning, by exploring the internalization of societal rules or how social emotions such as guilt, shame, and empathy mature as we grow older, aging studies present an alternative avenue for examining the mechanisms of moral reasoning. The latter approach provides us with an opportunity to study everyday examples of its breakdown; to explore, for instance, how these sophisticated socioemotional processes unravel in neurodegenerative disorders.

Frontotemporal Dementia (FTD) is a condition that is seen in older individuals less often than other forms of dementia like Alzheimer’s. Individuals with FTD, particularly the behavioural variant of FTD (bvFTD), show impaired moral reasoning, a commonly reported symptom. Individuals with bvFTD often behave in a manner that violates social norms, which in extreme cases can even result in criminal offences. Strikwerda-Brown and colleagues in their study published in the journal Brain (2021) investigated deviations in moral decision making in individuals with bvFTD. Strikwerda-Brown and others (2019) have also discussed the possible mechanisms behind such aberrations in greater detail in their recent review paper, ‘Neurocognitive mechanisms of theory of mind impairment in neurodegeneration: a transdiagnostic approach’. Alterations in moral reasoning in bvFTD have also been captured in the lab setting, using classic moral dilemma paradigms. Individuals with bvFTD tend to make increased utilitarian decisions in such situations, i.e., choosing to inflict personal harm on another individual in order to maximize their own aggregate welfare.


These atypical patterns of moral decision making in bvFTD were previously attributed to impaired emotional reasoning, due to atrophy in brain regions that support affective processing (e.g., the medial prefrontal cortex–mPFC). However, other cognitive processes such as conceptual knowledge have since also been shown to be affected in bvFTD, especially the knowledge of social rules and norms. Consequently, Strikwerda-Brown and fellow researchers were interested in examining how the loss of conceptual knowledge about socially acceptable standards of behaviour in bvFTD may affect moral decision making, and how this might in turn be reflected in the brain.


In a sample of twenty-six bvFTD patients, the researchers explored affective and social conceptual knowledge contributions to personal moral decision making, and identifying the underlying grey and white matter correlates of these processes using structural Magnetic Resonance Imaging (MRI) and diffusion-weighted MRI. In addition to completing a standard moral dilemma task, participants were required to report their immediate emotional reaction to each decision so as to directly probe their affective response. The researchers also administered a separate measure of social norms to assess conceptual knowledge.

This study is the first demonstration of its kind, where the results showed an impaired subjective emotional response to moral decisions in bvFTD patients who reported feeling significantly ‘better’ about their decisions than controls. Strikingly, most bvFTD patients reported feeling ‘extremely good’ about their decision of personally harming someone on at least one of the dilemmas. Individuals with bvFTD also displayed impaired knowledge of socially acceptable standards of behaviour, which significantly correlated with a more abnormal emotional response to the moral dilemmas, i.e., if one doesn’t know it’s wrong to harm others, they don’t feel bad about their decision.


A distributed network of brain regions was found to be associated with the abnormal affective responses to moral decisions, including reduced grey matter integrity in regions implicated in both affective (mPFC, insula) and conceptual (anterior temporal lobes–ATLs) processing. These neuroimaging findings corroborated quite well with the behavioural results, suggesting that both affective and conceptual processes may interact in the emotional response to moral dilemmas in bvFTD. But the researchers’ next question was–how? To investigate this, they looked to the white matter for plausible signs of evidence.


Specifically, they questioned whether the white matter pathways connecting frontal and temporal regions may support the relationship between affective and conceptual processing during moral decision making. Indeed, they found that reduced integrity of the uncinate fasciculus, which connects the mPFC to ATLs (see Figure 1), was associated with a more abnormal emotional response to moral decisions in individuals with bvFTD. This relationship was also partially explained by social conceptual knowledge.


The Uncinate Fasciculus (Mitsuhashi et al., 2009; Yeh et al., 2018)

In essence, the uncinate fasciculus may support emotional reactions to moral dilemmas by acting as a conduit between brain regions responsible for affective and conceptual processes. Degeneration of this tract in bvFTD could help explain the altered moral behaviours in this disorder. These findings have important implications for understanding and managing some of the challenging behaviours in bvFTD, and they might help pave the way for reducing the stigma attached to this disease as well as lay a foundation for targeted behavioural interventions in the near future.


(Disclaimer: Any views or opinions represented in this blog article are personal and belong solely to the author, and do not represent those of people, institutions or organizations that the author may be associated with in professional or personal capacity, unless explicitly stated.)


References

  1. Mitsuhashi, N., Fujieda, K., Tamura, T., Kawamoto, S., Takagi, T., & Okubo, K. (2009). BodyParts3D: 3D structure database for anatomical concepts. Nucleic Acids Research, 37(suppl_1), D782-D785. https://doi.org/10.1093/nar/gkn613

  2. Strikwerda-Brown, C., Ramanan, S., & Irish, M. (2019). Neurocognitive mechanisms of theory of mind impairment in neurodegeneration: a transdiagnostic approach. Neuropsychiatric Disease and Treatment, 15, 557–573. https://doi.org/10.2147/NDT.S158996

  3. Strikwerda-Brown, C., Ramanan, S., Goldberg, Z. L., Mothakunnel, A., Hodges, J. R., Ahmed, R. M., & Irish, M. (2021). The interplay of emotional and social conceptual processes during moral reasoning in frontotemporal dementia. Brain, 144(3), 938-952. https://doi.org/10.1093/brain/awaa435

  4. Yeh, F. C., Panesar, S., Fernandes, D., Meola, A., Yoshino, M., Fernandez-Miranda, J. C., ... & Verstynen, T. (2018). Population-averaged atlas of the macroscale human structural connectome and its network topology. NeuroImage, 178, 57-68. https://doi.org/10.1016/j.neuroimage.2018.05.027

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