Although a plethora of data exists on the role of the prefrontal cortex in memory retrieval, it has been difficult to relate specific aspects of retrieval processing to the different prefrontal regions. The present thesis consists of one behavioural experiment and three functional neuroimaging studies that aimed at elucidating the role of the mid-ventrolateral region of the prefrontal cortex in memory retrieval. We hypothesized that the mid-ventrolateral prefrontal cortex, through its anatomical connections with posterior association areas, is in a key position to exert control over posterior association areas where information is processed and stored for the active retrieval of mnemonic information. In contrast to automatic retrieval, active retrieval is necessary when a person retrieves based on his/her plans and intentions a specific memory amongst multiple related mnemonic traces. / Previously, we had demonstrated that the mid-ventrolateral prefrontal cortex in the right hemisphere controls active retrieval of non-verbal stimuli. More specifically, we reported activity increases within this region during the delay period that followed the presentation of a retrieval cue. We proposed that these activity increases reflect the top-down control exerted by the mid-ventrolateral prefrontal cortex to focus attention on relevant aspects of encoded memories in preparation for the decision. The first study of my thesis focuses on the behavioural correlates of this active retrieval process. The results indicate that the subjects' performance improves (i.e. becomes faster) with longer retrieval periods. Thus, some aspect of retrieval is initiated during the delay before the presentation of a test stimulus for the decision. The results, however, also indicate that retrieval continues after the presentation of the test stimulus. / The three event-related fMRI studies that make up chapters three, four, and five of the thesis were designed on the basis of the results obtained in the behavioural study described in chapter two. For all three fMRI studies, we used an experimental paradigm in which the retrieval cue coincided with the test stimulus presentation. The experimental design for the three neuroimaging studies was similar but examined the retrieval of mnemonic information from different sensory modalities. A separate group of subjects was tested for each study with a common hypothesis: when subjects are performing active retrieval trials, selective activity increases will be observed within the mid-ventrolateral prefrontal cortex. The study presented in chapter three examined verbal active retrieval, the study presented in chapter four examined tactile active retrieval, and the one in chapter five examined active retrieval for auditory stimuli. Selective activity increases were reported within the mid-ventrolateral prefrontal cortex during the active retrieval trials in all three studies. Activity increases were stronger in the left mid-ventrolateral prefrontal cortex when subjects retrieved verbal information. For tactile and auditory stimuli, the activity increases were bilateral. Importantly, within the prefrontal cortex, there were no other activity increases, indicating that the role of the mid-ventrolateral prefrontal cortex in memory retrieval is specific and distinct from that of other prefrontal regions. Thus it can be concluded that, across sensory modalities, the mid-ventrolateral prefrontal cortex plays a key role in the top-down control necessary for the disambiguation of information in memory during retrieval.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.115891 |
| Date | January 2008 |
| Creators | Kostopoulos, Penelope. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Psychology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002837801, proquestno: AAINR66678, Theses scanned by UMI/ProQuest. |
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