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For the past several years I am using neuroimaging to explore the brain mechanisms that control human cognition - particularly the nonconscious cognition. We conducted one of the first neuroimaging experiments on human memory and have localized the brain areas involved in nonconscious (implicit) and conscious (explicit) processing of human memory. These experiments have characterized the nature of processing that takes place in different brain areas (Badgaiyan, 2000b; Badgaiyan & Posner, 1996; Badgaiyan & Posner, 1997; Badgaiyan, Schacter, & Alpert, 1999; Schacter & Badgaiyan, 2001) and demonstrated that distinct neural circuits are involved in the processing of conscious and nonconscious memories. In addition, we traced the timeline of neural activations (for the first time) to enhance our understanding of these circuits. Based on the data acquired in these experiments we proposed that a small extrastriatal areas (area V3A) is critically involved in multimodal processing of implicit memory. To characterize the nature of processing in this area, we conducted further experiments. These experiments included first neuroimaging study of the auditory and cross-modal priming (Schacter, Badgaiyan, & Alpert, 1999; Badgaiyan, Schacter, & Alpert, 1999; Badgaiyan, Schacter, & Alpert, 2001). The data acquired in these experiments demonstrated the modal independence of the area V3A and clarified that the reduced extrastriatal activations observed in the priming experiments, is not related to visual information processing, as suggested by a number of investigators. In the study of cross modal priming, implicitly acquired visual information was retrieved using auditory cues and aurally studied items were retrieved visually. Finding of reduced activation in the extrastriatal area in both of these experiments confirmed that the reduction is related specifically to implicit memory processing. In addition, increased activation in the primary auditory cortex observed in auditory to visual cross modal priming and in auditory priming experiments revealed that the areas associated with the processing of primed stimuli are also a part of the neural circuit of nonconscious memory. Using these data, we were able to formulate a comprehensive neurocognitive model of implicit memory (Schacter & Badgaiyan, 2001). In another series of experiments we demonstrated simultaneous activation of different areas of the cingulate cortex during processing of two components of the central executive: response selection and error monitoring (Badgaiyan & Posner, 1998). This experiment suggested that different components of the central executive are processed by distinct neuronal clusters. This finding was important because it was the first serious challenge to a widely held inaccurate concept concerning processing of central executive functions. The concept suggested that all of these functions are processed in the anterior cingulate cortex. In addition, the data acquired in this experiment defined the role of the frontal cortex in executive processing and demonstrated how the frontal and cingulate cortices interact during the processing. The finding of this experiment helped me formulate a neural model of the brain executive system (Badgaiyan, 2000a). This model is a part of the curricula of a number of institutions. Another important contribution of our study concerns the nature of stimuli that elicit cognitive processing. A number of investigators have suggested that a stimulus can elicit cognitive processing only if it is consciously perceived and analyzed. This suggestion however is not consistent with the ability of subliminal stimuli that initiate cognitive processing without being consciously perceived. Since cognitive studies were unable to arrive at a conclusion concerning the nature of stimuli, we conducted a neuroimaging experiment. In this experiment we observed that the pattern of cortical activation elicited by the stimuli that are not consciously perceived is similar to the pattern elicited by consciously perceived stimuli in a memory task. The experiment therefore provided convincing evidence to indicate that conscious perception of stimuli is not necessary for initiation of cognitive processing (Badgaiyan, 2000b; Badgaiyan, Schacter, & Alpert, 2001). In another series of experiments we studied the conscious and nonconscious associative functions (Badgaiyan, Schacter, & Alpert, 2002; Badgaiyan, Schacter, & Alpert, 2003). While revealing that distinct neural circuits are involved in the processing of conscious and nonconscious associative memories, these experiments characterized the role of ventral prefrontal cortex in the formation of associations, which is a necessary component of human memory. A consistent theme of my research centered around understanding of the neural elements of conscious processing. Explicit representatives of these studies include exploration of the neural [processing associated with nonconscious and conscious processing (Badgaiyan, 2002a; Badgaiyan, 2002b; Badgaiyan, 2005a; Badgaiyan, 2005b; Badgaiyan, 2006) While conducting these studies I became aware of the extremely limited ability of neuroimaging techniques to detect neurochemical change associated with cognitive processing. I therefore, developed a molecular imaging technique that allows detection, mapping and measurement of dopamine released during cognitive task performances. Using this technique we have, for the first time detected dopamine released during processing of a number of cognitive and behavioral tasks (Badgaiyan, Alpert, & Fischman, 2003; Alpert, Badgaiyan, Livini, & Fischman, 2003; Badgaiyan, Fischman, & Alpert, 2003; Badgaiyan, Fischman, & Alpert, 2005; Badgaiyan, 2006; Badgaiyan, Alpert, & Fischman, 2006; Badgaiyan, Fischman, & Alpert, 2006; Fischman & Badgaiyan, 2006; Badgaiyan, Fischman, & Alpert, 2007d; Badgaiyan, Fischman, & Alpert, 2007c; Badgaiyan, Fischman, & Alpert, 2007b; Badgaiyan, Fischman, & Alpert, 2007a; Fischman & Badgaiyan, 2007; Badgaiyan, Fischman, & Alpert, 2008a; Badgaiyan, Fischman, & Alpert, 2008b). This technique has extended the scope of cognitive and psychiatric research by allowing investigation of an unexplored aspect (neurochemistry) of human cognition. Further, to examine the ability of modified molecular imaging to explore pathophysiology of psychiatric and neurological conditions, we recently modified the technique further, and studied neurocognitive deficits in PTSD and ADHD patients. The data acquired in these experiments provided novel insight into the neurocognitive deficit and can be used for developing objective diagnostic criteria. More significantly, because these experiments have objectively defined the neural deficits, the data could be used for early diagnosis and for development of novel therapeutic strategies. We are currently developing the next generation of the dynamic molecular imaging that would allow simultaneous detection of changes in multiple neurotransmitters and neuromodulators during a cognitive task performance. Bibliography Alpert, N. M., Badgaiyan, R. D., Livini, E., & Fischman, A. J. (2003). A novel method for noninvasive detection of neuromodulatory changes in specific neurotransmitter systems. NeuroImage, 19(3), 1049-1060. Badgaiyan, R. D. (2000a). Executive control, willed actions, and nonconscious processing. Hum Brain Mapp, 9(1), 38-41. Badgaiyan, R. D. (2000b). Neuroanatomical organization of perceptual memory: an fMRI study of picture priming. Hum Brain Mapp, 10(4), 197-203. Badgaiyan, R. D. (2002a). Cognitive processing of nonconscious stimuli: An fMRI study. Paper presented at the American Psychiatric Association, Philadelphia. Badgaiyan, R. D. (2002b). Nonconscious processing, anterior cingulate, and catatonia. Behavioral and Brain Sciences, 25, Behavioral and Brain Sciences, 578-579. Badgaiyan, R. D. (2005a). Conscious awareness and the brain processing. Elements, 3, 8-12. Badgaiyan, R. D. (2005b). Conscious awareness of retrieval: an exploration of the cortical connectivity. Int J Psychophysiol, 55(2), 257-262. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2007a). Detection of task-induced release of extrastriatal dopamine using fallypride. Paper presented at the Journal of Nuclear Medicine, Washington, DC. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2007b). Striatal dopamine release during emotional memory processing. Paper presented at the Journal of Nuclear Medicine, Washington, DC. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2008a). Phasic Release of Striatal Dopamine During Response Inhibition. Paper presented at the European association of nuclear medicine. Badgaiyan, R. D. & Posner, M. I. (1996). Priming reduces input activity in right posterior cortex during stem completion. Neuroreport, 7(18), 2975-2978. Badgaiyan, R. D. & Posner, M. I. (1997). Time course of cortical activations in implicit and explicit recall. J Neurosci, 17(12), 4904-4913. Badgaiyan, R. D. & Posner, M. I. (1998). Mapping the cingulate cortex in response selection and monitoring. Neuroimage, 7(3), 255-260. Badgaiyan, R. D., Schacter, D. L., & Alpert, N. M. (1999). Auditory Priming within and across Modalities: Evidence from Positron Emission Tomography. J Cogn Neurosci, 11(4), 337-348. Badgaiyan, R. D., Schacter, D. L., & Alpert, N. M. (2001). Priming within and across Modalities: Exploring the Nature of rCBF Increases and Decreases. Neuroimage, 13(2), 272-282. Badgaiyan, R. D., Schacter, D. L., & Alpert, N. M. (2002). Retrieval of relational information: a role for the left inferior prefrontal cortex. Neuroimage, 17(1), 393-400. Badgaiyan, R. D., Schacter, D. L., & Alpert, N. M. (2003). Priming of new associations: a PET study. Neuroreport, 14(18), 2475-2479. Badgaiyan, R. D., Alpert, N. M., & Fischman, A. J. (2003). Detection of striatal dopamine release during a motor planning task in human volunteers. Paper presented at the J. Cerebral Blood Flow and Metabolism, Calgery, Canada. Badgaiyan, R. D., Alpert, N. M., & Fischman, A. J. (2006). Neurochemical Mapping of Human Cognition. Paper presented at the NeuroImage, Florence, Italy. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2003). Striatal dopamine release during unrewarded motor task in human volunteers. Neuroreport, 14(11), 1421-1424. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2005). Detection of striatal dopamine released during an explicit motor memory task. Paper presented at the Journal of Nuclear Medicine. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2006). Striatal Dopamine Release During a Cued-Recall Task. Paper presented at the Journal of Nuclear Medicine, San Diesgo. Badgaiyan, R. D., Fischman, A. J., & Alpert, N. M. (2007c). Detection of Extrastriatal Dopamine Release in Healthy Human Volunteers. Paper presented at the 23rd International Symposium on Cerebral Blood Flow and Metabolism and the 8th International Conference on Quantification of Brain Function with PET (Brain’07), Osaka; Japan. |