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The neural organization of memory

The research specifically focused on the role of medial temporal, ventromedial prefrontal, and dorsolateral prefrontal regions in the mediation of various memory functions. A series of investigations were performed on patients with focal brain lesions localized in the mentioned areas. It was possible to identify the specific contribution of these areas to memory. Both medial temporal and ventromedial prefrontal regions were found to be involved in the retention of image-based representation of objects, as well as in the new learning of visual objects. Moreover, right-hemispheric specialization in these functions was found. On the other hand, both the ventromedial prefrontal and dorsolateral prefrontal regions contributed to the organizational aspects of memory, such as strategic search processes. These findings support the view that discrete regions of the brain subserve different aspects of memory. Furthermore, the ventromedial prefrontal cortex seems to form a nexus which integrates several memory-related processes.

In another study, our goal was to clarify the role of the orbitofrontal cortex (OFC) in cognitive inhibition by examining the effects of focal lesions to the medial OFC (posterior part of the gyrus rectus) on performance on several tasks that required inhibitory control. The study indicated a specific contribution of the medial OFC to lower-order inhibitory processes such as response inhibition and stimulus-based switching of attention. As inhibition is considered an executive function essential for both working memory and long-term memory performance, it is possible to speculate that memory problems emerging after medial OFC lesions are partly caused by defective inhibition processes.

Primate neurophysiological studies suggest that the OFC is also a possible source of motivational influence upon cognitive control and that this region may relay motivationally significant information to the dorsolateral prefrontal cortex (DLPFC) (Wallis JD, Miller EK. Neuronal activity in primate dorsolateral and orbital prefrontal cortex during performance of a reward preference task. Eur J Neurosci. 2003, 18, 2069-2081; Hikosaka K, Watanabe M. Delay activity of orbital and lateral prefrontal neurons of the monkey varying with different rewards. Cerebral Cortex, 2000, 10, 263-271). Our recent study concerned this issue. We used two complementary approaches: neuroimaging study on healthy human subjects (experiment I) and behavioural study on brain-damaged subjects (experiment II). In experiment I we investigated the effective connectivity between prefrontal regions of human brain supporting motivational influence on working memory. Functional magnetic resonance imaging (fMRI) and structural equation modeling (SEM) were used to examin the interaction between the lateral OFC, medial OFC, and DLPFC regions in the right and left hemisphere during performance of verbal 2-back working memory task under two motivational conditions. The “high-motivation” condition involved the probability of winning or losing a certain amount of money, while the “low-motivation” condition was not associated with monetary reinforcement. In the “low-motivation” condition, the OFC regions in both hemispheres positively influenced the left DLPFC activity. In the “high-motivation” condition, the connectivity in the network including the right OFC regions and left DLPFC changed from positive to negative, whereas the positive connectivity in the network composed of the left OFC and left DLPFC became slightly enhanced compared with the “low-motivation” condition. Condition-dependent changes in effective connectivity between the OFC regions and the left DLPFC appear to be the functional correlate of motivational influence on verbal working memory.

Experiment II was conducted to further evaluate the role of the OFC in the motivational modulation of cognition by examining the effects of focal unilateral lesions to the medial OFC on the performance on an incentive working memory task. Participants performed a 2-back working memory task under three motivational conditions (punishment-, reward-, and no-incentive). The results suggest that the right and left medial OFCs support the influence of punishment- and reward-motivation on working memory, respectively.

Szatkowska I., Szymańska O., Marchewka A., Soluch P., Rymarczyk K. Dissociable contributions of the left and right posterior medial orbitofrontal cortex in motivational control of goal-directed behavior. Neurobiology of Learning and Memory, 96 (2): 385-391, 2011

Szatkowska I.,Szymańska O., Marchewka A., Soluch P. The effect of motivation on working memory: A role of medial orbitofrontal cortex. (poster presentation, 41st European Brain and Behaviour Society Meeting, 2009)

Szatkowska I, Bogorodzki P, Wolak T, Marchewka A, Szeszkowski W. The effect of motivation on working memory: An fMRI and SEM study. Neurobiology of Learning and Memory, 90, 475-478, 2008

Szatkowska I, Szymańska O, Bojarski P, Grabowska A.  Cognitive inhibition in patients with medial orbitofrontal damage. Experimental Brain Research, 181, 109-115., 2007

Szatkowska I, Szymańska O, Grabowska A. The role of the human ventromedial prefrontal cortex in memory for contextual information. Neuroscience Letters, 364(2): 71-75, 2004

Szatkowska I, Grabowska A, Szymańska O. Memory for object and object-location after lesions to the ventromedial prefrontal cortex in humans. Acta Neurobiologiae Experimentalis, 63: 31-38, 2003

Szatkowska I, Grabowska A, Szymańska O. Evidence for the involvement of the ventro-medial prefrontal cortex in a short-term storage of visual images. Neuroreport, 12: 1187-1190, 2001

Szatkowska I, Grabowska A, Szymańska O. Phonological and semantic fluencies are mediated by different regions of the prefrontal cortex. Acta Neurobiologiae Experimentalis, 60: 503-508, 2000

Szatkowska I, Szymańska O, Bednarek D, Skowrońska R, Grabowska A. Disturbances in time limited storage of sensory information after right temporal lobectomy. Acta Neurobiologiae Experimentalis, 56: 259-262, 1996

Grabowska A, Łuczywek E, Fersten E, Herman A, Szatkowska I. Memory impairmnet in patients with stereotaxic lesions to the hippocampus and amygdala. Acta Neurobiologiae Experimentalis, 54: 393-403, 1994

 

 

Nencki Institute of Experimental Biology (c) 2015