Dr. Cassidy’s research program is focused on using multimodal neuroimaging methods to understand brain mechanisms of psychopathology. He has a long-standing interest in the role of the dopamine system in reward processing in schizophrenia and addiction. His graduate training at McGill University was focused on basic neuroscience (MSc) and clinical research (PhD) in schizophrenia. He completed postdoctoral training focused on neuroimaging methods at Columbia University within the Division of Translational Imaging under the mentorship of Anissa Abi-Dargham and Guillermo Horga.
Since arriving in Ottawa in 2016, Dr. Cassidy has continued his neuroimaging work in schizophrenia and expanded to the study of PTSD and other neuropsychiatric conditions. His goal is to bridge the gap between the problems faced by individuals with mental illness and the technical challenges of understanding brain function. By bringing his expertise in these two disparate questions he strives towards a more scientific understanding of human experience. Such insights serve to advance neuroscience and could also improve mental health outcomes, particularly when they can explain psychiatric risk or improve strategies for early intervention and prevention of conditions such as PTSD and schizophrenia.
Neuromelanin-sensitive imaging of the substantia nigra and locus coeruleus
The neurotransmitters dopamine and noradrenalin are released from neurons located in the substantia nigra and locus coeruleus respectively. These structures have the unique property of containing high concentrations of neuromelanin, a dark pigment that can be visualized with specialized MRI sequences. The neuromelanin-sensitive MRI signal has been used to visualize degeneration of these neurons in Parkinson’s disease and healthy aging. Our recent work has shown that this signal can also serve as a proxy measure for long-term imbalance in activity of these neurotransmitter systems. Current projects are investigating this novel measure as a potential biomarker in diverse populations including, schizophrenia, individuals at-risk of schizophrenia, Parkinson’s disease, addiction, PTSD, and healthy aging. Other work uses dopamine PET imaging and post-mortem midbrain tissue to better validate this technique and interpret the neuromelanin MRI signal.
- Cassidy CM, Zucca F, Girgis R, Baker S, Weinstein J, Sharp M, Bellei C, Valmadre A, Vanegas N, Kegeles LS, Brucato G, Kang UJ, Sulzer D, Zecca L, Abi-Dargham A, Horga G (2019). Neuromelanin-sensitive MRI as a non-invasive proxy measure of dopamine function in the human brain. Proceedings of the National Academy of Sciences of the United States. epub
- Cassidy CM, Balsam PD, Weinstein JJ, Rosengard RJ, Slifstein M, Daw ND, Abi-Dargham A, Horga G (2018). A perceptual inference mechanism for hallucinations linked to striatal dopamine. Current Biology 28: 503-514.
- Sulzer D,Cassidy C, Horga G, Kang U, Fahn S, Casella L, Pezzoli G, Langley J, Hu X, Zucca F, Isaias I, Zecca L (2018) Neuromelanin detection by magnetic resonance imaging (MRI) and its promise as a biomarker for Parkinson’s disease. npj Parkinon’s Disease epub.
- Cassidy CM, Van Snellenberg JX, Benavides C, Slifstein M, Wang, Moore H, Abi-Dargham A, Horga G (2016) Dynamic Connectivity between Brain Networks Supports Working Memory: relationships to Dopamine Release and Schizophrenia The Journal of Neuroscience 36 (15): 4377-4388.
- Van de Giessen E, Weinstein JJ, Cassidy CM, Haney M, Dong Z, Ghazzaoui R, Ojeil N, Kegeles LS, Xu X, Vadhan NP, Volkow N, Slifstein M, Abi-Dargham A (2016) Deficits in striatal dopamine release in cannabis dependence. Molecular Psychiatry 22(1): 68-75.
- Horga G, Cassidy CM, Xu X, Moore H, Slifstein M, Van Snellenberg JX, Abi-Dargham A (2016) Dopamine-related disruption of functional topography of striatal connections in unmedicated patients with schizophrenia. JAMA Psychiatry 73(8): 862-70.
- Cassidy CM, Brodeur M, Lepage M, Malla A. (2014) Do reward processing deficits in schizophrenia-spectrum disorders promote cannabis use? An investigation of physiological response to natural rewards and drug cues. Journal of Psychiatry and Neuroscience. 39(5):339-47.
- Cassidy CM, Lepage M, Malla A. (2014) Do motivation deficits in schizophrenia-spectrum disorders promote cannabis use? An investigation of behavioural response to natural rewards and drug cues. Psychiatry Research. 215(3): 522-7.
- Cassidy CM, Buchy L, Bodnar M, Dell’Elce J, Choudhry Z, Fathalli F, Fox R, Sengupta S, Iyer S, Malla A, Lepage M, Joober R (2014). Association of a risk allele of ANK3 with lower cognitive performance and cortical thinning in patients with first episode psychosis. Journal of Psychiatry and Neuroscience. 39(1):31-9.
- Albanna A, Choudhry Z, Harvey PO, Fathalli F, Cassidy C, Sengupta SM, Iyer SN, Rho A, Lepage M, Malla A, Joober R. (2014) TCF4 gene polymorphism and cognitive performance in patients with first episode psychosis. Schizophrenia Research. 152(1):124-9.
- Cassidy CM, Harvey P, Lepage M, Malla AK. (2012) Cannabis use and anticipatory pleasure as reported by subjects with early psychosis and community controls. Schizophrenia Research. 137(1-3):39-44.
- Cassidy CM, Joober R, King S, Malla AK. (2011) Childhood symptoms of inattention-hyperactivity predict cannabis use in first episode psychosis. Schizophrenia Research; 132(2-3):171-6.
- Cassidy CM, Norman R, Manchanda R, Schmitz N, Malla, A. (2010) Testing definitions of symptom remission in first episode psychosis for prediction of functional outcome at two years. Schizophrenia Bulletin; 36(5):1001-8.
- Cassidy CM, Rabinovitch M, Schmitz N, Joober R, Malla A. (2010) A comparison study of multiple measures of adherence to antipsychotic medication in first-episode psychosis. Journal of Clinical Psychopharmacology; 30(1):64-7.
- Cassidy CM, Quirion R, Srivastava LK (2006). Blockade of presynaptic voltage-gated calcium channels in the medial prefrontal cortex of neonatal rats leads to post-pubertal behavioural alterations. Brain Research;1083(1):164-73.