WHAT CATATONIA CAN TELL US ABOUT "TOP-DOWN MODULATION": A NEUROPSYCHIATRIC HYPOTHESIS

Abstract

Differentialdiagnosis of motor symptoms, as for example akinesia, may be difficult since they may be either of neurologic, as for example Parkinson’s, or psychiatric, as for example catatonia, origin leading to a so-called „conflict of paradigms“. Despite different origins such symptoms may clinically be more or less similar which may reflect functional brain organisation in general and cortical-subcortical relations in particular. It is therefore hypothesized that similarities and differences between Parkinson’s as a motor disorder and catatonia as a psychomotor disorder may be accounted for by functional differences between „top-down modulation“ and „bottom-up modulation“ between prefrontal/frontal cortex and basal ganglia implying double dissociation between both diseases with regard to underlying pathophysiology. Catatonia can be characterized by concomittant motor, emotional, and behavioral symptoms which may be accounted for by dysfunction in orbitofrontal-prefrontal/parietal cortical connectivity as a form of „horizontal i.e. cortico-cortical modulation“. Furthermore alteration in „top-down modulation“ of caudate and other basal ganglia by gaba-ergic mediated orbitofrontal cortical deficits may account for motor symptoms in catatonia. Parkinson’s in contrast can be characterized by predominant motor symptoms which may be accounted for by altered „bottom-up modulation“ between dopaminergic mediated deficits in striatum and premotor/motor cortex. Due to connectional asymmetry i.e. unidirectionality in prefronto-premotor/motor cortical connections, there is no further dysregulation in other prefrontal cortical areas in Parkinson’s as it is reflected in absence of major psychiatric symptoms in such patients. It is concluded that comparison between Parkinson’s and catatonia may reveal the nature of both „top-down modulation“ and „bottom-up modulation“ in further detail. Furthermore difference between Parkinson’s as a motor and catatonia as a psychomotor disorder may be accounted for by pecularities in „horizontal i.e. cortico-cortical modulation“ which, unlike „top-down and bottom-up modulation“ as forms of „vertical modulation“, may be unidirectional and thus asymmetric not allowing for direct modulation of prefrontal cortical areas by premotor/motor cortex. Key-words: Catatonia - Parkinson’s - Top-down modulation - Bottom-up modulation - Horizontal modulation Differentialdiagnosis of motor symptoms, as for example akinesia, may be difficult since they may be either of neurologic, as for example Parkinson’s, or psychiatric, as for example catatonia, origin leading to a so-called „conflict of paradigms“. Despite different origins such symptoms may clinically be more or less similar which may reflect functional brain organisation in general and cortical-subcortical relations in particular. It is therefore hypothesized that similarities and differences between Parkinson’s as a motor disorder and catatonia as a psychomotor disorder may be accounted for by functional differences between „top-down modulation“ and „bottom-up modulation“ between prefrontal/frontal cortex and basal ganglia implying double dissociation between both diseases with regard to underlying pathophysiology. It is concluded that comparison between Parkinson’s and catatonia may reveal the nature of both „top-down modulation“ and „bottom-up modulation“ in further detail. Furthermore difference between Parkinson’s as a motor and catatonia as a psychomotor disorder may be accounted for by pecularities in „horizontal i.e. cortico-cortical modulation“ which, unlike „top-down and bottom-up modulation“ as forms of „vertical modulation“, may be unidirectional and thus asymmetric not allowing for direct modulation of prefrontal cortical areas by premotor/motor cortex.