fMRI and patient studies of remote spatial and episodic memory

点击翻译按钮获取中文摘要

Remembering past personal experiences (episodic memory) and how to get around in our home or neighbourhood (spatial memory) are both crucial for daily life. Without episodic memory, we are unable to re-experience our most cherished moments or to recall critical information that may be necessary to everyday function; without spatial memory, we literally would be lost. This proposal is concerned with how these types of memories relate to one another and how they are represented in the brain. Our ability to learn and retain new episodic and spatial memories depends on the hippocampus, a structure deep in the temporal lobes: damage to the hippocampus impairs memory for recently experienced events and spatial environments. With the support of a previous NSERC grant, my students and I showed that with the passage of time, episodic and spatial memories that are highly detailed and precise continue to depend on the hippocampus. We also showed that the role of the hippocampus extends beyond memory to include the ability to imagine detailed future episodes that have not yet occurred. In contrast, more schematic or coarse spatial memories of very familiar environments (i.e., a skeletal “map” of major roads and landmarks) do not appear to depend on the hippocampus and instead rely on other brain structures. One of these brain structures that we identified is within the back portion of the parietal lobes. The goal of the current proposal is to investigate several related questions: 1) Is the role of the hippocampus in supporting different types of memories and future experiences simply a reflection of a more basic function that is common to all of these abilities, or are these abilities represented in separate parts of the hippocampus? 2) How do the hippocampus and parietal lobes contribute to spatial memories of very familiar environments? 3) Can other brain regions “come to the rescue” and support some aspects of spatial memory when the hippocampus or parietal lobes are not functioning well? Studies are designed to answer these questions by testing the ability to remember past experiences, imagine future experiences, and make decisions about well-known landmarks, including their appearance and the distances, directions, and routes between them. We take an innovative approach of scanning expert and non-experts, older adults, and individuals with damage to the parietal lobes using functional magnetic resonance imaging (fMRI), a technique that allows visualization of on-line brain activity (blood flow) as participants perform the various tasks. Study 1 will involve scanning a unique population of experts, birdwatchers, who keep journals of the time and spatial location of birds that they have encountered in the past. Journals also serve as a record of birds that have not yet been encountered, allowing us to directly compare the role of the hippocampus in episodic memory for the spatial or temporal context of bird sightings or future imagining of bird sightings that have not yet taken place. Study 2 involves scanning older adults who experience changes to the hippocampus and patients with lesions to the parietal lobes. The two groups have different memory profiles that allow for the study of different components of spatial memory. Canada has a rich history in the area of cognitive neuroscience and continues to be regarded as an international leader in memory research. It is important to maintain this status through the specialized training of students in developing basic theory and effective applications of innovative technologies such as fMRI for examining brain function. Findings from this research will lead to a greater understanding of the cognitive makeup of different types of memory and how they are represented in the human brain.