fa Behavioral Neuroscience Behavioral Neuroscience Original Original <p style="text-align: justify;"><strong>Introduction:</strong> A fixed hemodynamic response function (HRF) is commonly used for functional&nbsp;magnetic resonance imaging (fMRI) analysis. However, HRF may vary from region to region&nbsp;and subject to subject. We investigated the effect of locally estimated HRF (in functionally&nbsp;homogenous parcels) on activation detection sensitivity in a heroin cue reactivity study.<br> <strong>Methods: </strong>We proposed a novel exploratory method for brain parcellation based on a probabilistic&nbsp;model to segregate the brain into spatially connected and functionally homogeneous components.&nbsp;Then, we estimated HRF and detected activated regions in response to an experimental task in&nbsp;each parcel using a joint detection estimation (JDE) method. We compared the proposed JDE&nbsp;method with the general linear model (GLM) that uses a fixed HRF and is implemented in FEAT&nbsp;(as a part of FMRIB Software Library, version 4.1).<br> <strong>Results:</strong> 1) Regions detected by JDE are larger than those detected by fixed HRF, 2) In group&nbsp;analysis, JDE found areas of activation not detected by fixed HRF. It detected drug craving&nbsp;a priori &ldquo;regions-of-interest&rdquo; in the limbic lobe (anterior cingulate cortex [ACC], posterior&nbsp;cingulate cortex [PCC] and cingulate gyrus), basal ganglia, especially striatum (putamen and<br> head of caudate), and cerebellum in addition to the areas detected by the fixed HRF method, 3)&nbsp;JDE obtained higher Z-values of local maxima compared to those obtained by fixed HRF.<br> <strong>Conclusion:</strong> In our study of heroin cue reactivity, our proposed method (that estimates HRF&nbsp;locally) outperformed the conventional GLM that uses a fixed HRF.</p> functional Magnetic Resonance Imaging (fMRI), Parcellation, Hemodynamic Response Function (HRF), Cue reactivity, Heroin 299 314 http://bcn.iums.ac.ir/browse.php?a_code=A-10-992-4&slc_lang=fa&sid=1 Somayeh Maleki-Balajoo 1370031947532846008545 1370031947532846008545 No Department of Biomedical Engineering, Faculty of Electrical Engineering, Khaje Nasir Toosi University of Technology, Tehran, Iran. Gholam-Ali Hossein-Zadeh 1370031947532846008546 1370031947532846008546 No Control and Intelligent Processing Center of Excellence, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran. Hamid Soltanian-Zadeh hszadeh@ut.ac.ir 1370031947532846008547 1370031947532846008547 Yes Control and Intelligent Processing Center of Excellence, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran. Hamed Ekhtiari 1370031947532846008548 1370031947532846008548 No Research Center for Cellular and Molecular Imaging, Tehran University of Medical Sciences, Tehran, Iran.