Abstract
The Stria Medullaris (SM) is a white-matter tract that contains afferent fibres that connect the cognitive-emotional areas in the forebrain to the Habenula (Hb). The Hb plays an important role in behavioral responses to reward, stress, anxiety, pain, and sleep through its action on neuromodulator systems. The Fasciculus Retroflexus (FR) forms the primary output of the Hb to the midbrain. The SM, Hb, and FR are part of a special pathway between the forebrain and the midbrain known as the Dorsal Diencephalic Conduction system (DDC). Hb dysfunction is accompanied by different types of neuropsychiatric disorders, such as schizophrenia, depression, and Treatment-Resistant Depression (TRD). Due to difficulties in the imaging assessment of the SM and HB in vivo, they had not been a focus of clinical studies until the invention of Diffusion Tensor Imaging (DTI), which has revolutionized the imaging and investigation of the SM and Hb. DTI has facilitated the imaging of the SM and Hb and has provided insights into their properties through the investigation of their monoamine dysregulation. DTI is a well-established technique for mapping brain microstructure and white matter tracts; it provides indirect information about the microstructural architecture and integrity of white matter in vivo, based on water diffusion properties in the intra- and extracellular space, such as Axial Diffusivity (AD), Radial Diffusivity (RD), mean diffusivity, and Fractional Anisotropy (FA). Neurosurgeons have recognized the potential value of DTI in the direct anatomical targeting of the SM and Hb prior to Deep Brain Stimulation (DBS) surgery for the treatment of certain neuropsychiatric conditions, such as TRD. DTI is the only non-invasive method that offers the possibility of visualization in vivo of the white-matter tracts and nuclei in the human brain. This review study summarizes the use of DTI as a promising new imaging method for accurate identification of the SM and Hb, with special emphasis on direct anatomical targeting of the SM and Hb prior to DBS surgery.
Highlights
The Dorsal Diencephalic Conduction System (DDCS) is a highly conserved integrative and modulatory pathway that is present in all vertebrates
Probabilistic Diffusion Tensor Imaging (DTI) was applied to 10 patients with Mass Intermedia (MI) seen in MRI
The Stria Medullaris (SM) was reliably seen in all 10 subjects with evidence that the SM fibres crossed to the ipsilateral hemisphere
Summary
The Dorsal Diencephalic Conduction System (DDCS) is a highly conserved integrative and modulatory pathway that is present in all vertebrates. The DDCS is a pathway that transmits information from the cognitive-emotional forebrain to the regulatory midbrain areas It is composed of three structures: the Stria Medullaris (SM), the Habenula (Hb), and the Fasciculus Retroflexus (FR) [1] (Fig. 1). It is challenging to render it accurately with DTI tractography because it is short, thin, and highly curved It is imbedded deep within brain tissue, so it is not easy to isolate from the surrounding white matter structures. The application of DTI tractography for accurate imaging of the SM could lead to a greater understanding of psychiatric neuropathology, addiction, and pain disorders through the analysis of its diffusion metrics.
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