The truth about cognitive impairment in functional motor symptoms: An experimental deception study with the Guilty Knowledge Task

Background: A century ago, Janet was the first to conceptualize conversion reactions as having a neurocognitive component, as disorders of memory processing that arise in the wake of trauma. The available evidence suggests that this impairment might arise from dysfunction in the fronto-subcortical circuits. Our aim was to examine the cognitive functions regulating deception in patients with functional motor symptoms (FMS), using a computerised task, the Guilty Knowledge Task (GKT). We also tested a group of healthy subjects (HS) as a control group. Materials and methods: Thirteen patients affected by FMS and 14 HS underwent a modified version of the GKT, a computer-controlled procedure used to detect truthful and deceptive responses. All participants were also screened for depression, anxiety, alexithymia and for moral sense (moral judgment task). Results: The reaction times (RTs) were significantly longer for lie responses than for true responses (F (1,26) = 50.47; p < 0.001) in the two groups. Total RTs were significantly longer for patients with FMS than for HS, in true responses (F(1,25) = 4,36; p = 0.047) and lie responses (F(1,25) = 4.26; p = 0.05). No differences were found between the two groups for accuracy in producing true responses (F(1,25) = 0.09, p = 0.77), and lie responses (F(1,25) = 0,12, p = 0.73. Conclusions: When tested with the GKT, patients with FMS were slower than HS in producing truthful and lying responses. Current knowledge along with our new findings in patients with FMS - possibly arising from individually unrecognised extremely mild, cognitive difficulties - should help in designing specific rehabilitative programmes to improve cognitive and behavioural disturbances in these patients.