Abstract
Substantia nigra/ventral tegmental area (SN/VTA) subregions, defined by dopaminergic projections to the striatum, are differentially affected by health (e.g. normal aging) and disease (e.g. Parkinson's disease). This may have an impact on reward processing which relies on dopaminergic regions and circuits. We acquired diffusion tensor imaging (DTI) with probabilistic tractography in 30 healthy older adults to determine whether subregions of the SN/VTA could be delineated based on anatomical connectivity to the striatum. We found that a dorsomedial region of the SN/VTA preferentially connected to the ventral striatum whereas a more ventrolateral region connected to the dorsal striatum. These SN/VTA subregions could be characterised by differences in quantitative structural imaging parameters, suggesting different underlying tissue properties. We also observed that these connectivity patterns differentially mapped onto reward dependence personality trait. We show that tractography can be used to parcellate the SN/VTA into anatomically plausible and behaviourally meaningful compartments, an approach that may help future studies to provide a more fine-grained synopsis of pathological changes in the dopaminergic midbrain and their functional impact.
Highlights
The anatomical topology of the Substantia nigra/ventral tegmental area (SN/VTA) can be defined by dopaminergic projections to the striatum
We acquired diffusion tensor imaging (DTI) with probabilistic tractography in 30 healthy older adults to determine whether subregions of the SN/VTA could be delineated based on anatomical connectivity to the striatum
Visual inspection of the results in each subject revealed that a more dorsomedial region of the SN/VTA was defined by connectivity to the ventral striatum whereas a more ventrolateral region of the SN/ VTA was defined by connectivity to the dorsal striatum (Fig. 1B)
Summary
The anatomical topology of the SN/VTA can be defined by dopaminergic projections to the striatum. An alternative approach is to use diffusion tensor imaging (DTI) and probabilistic tractography to segment structures based on their regional connectivity (Behrens and Johansen-Berg, 2005). DTI is a structural neuroimaging technique sensitive to the direction of water diffusion in tissues (Mori and Zhang, 2006; Moseley et al, 1990). This approach has been used to parcellate a range of cortical and subcortical structures (Behrens et al, 2003; Draganski et al, 2008; Johansen-Berg et al, 2008; Lambert et al, 2012; Menke et al, 2010; Rushworth et al, 2006). DTI-derived connectivity maps have close correspondence to the underlying cytoarchitectonics derived from post-mortem data (Klein et al, 2007; Seehaus et al, 2012) and relate to interindividual differences in personality and behaviour (Cohen et al, 2009; Forstmann et al, 2011, 2012)
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