9.081 Lecture 1 Notes

What is Memory? Memory proper…is the knowledge of a former state of mind after it has already once dropped from consciousness; or rather it is the knowledge of an event, or fact, of which meantime we have not been thinking, with the additional consciousness that we have thought or experienced it before. Forms of Memory • remembering details of the last movie you saw H.M. and the Amnesic Syndrome Patient H.M. 1926 born 1942 first major seizure (age 16) 1953 bilateral medial-temporal lobe resection (hippocampus & nearby structures) 1955 first published report of pervasive and profound anterograde amnesia 1962 neuropsychological examinations characterizing the amnesic syndrome Medial Temporal Lobe Lesions & Amnesia Forms of Memory • riding a bike or showboarding Forms of Memory • increased probability of using a word, phrase, or concept that has recently been uttered What is Memory? A change in the system, brought about by experience, that influences subsequent processes Learning & Memory Learning • the processes by which changes occur as a result of experience Memory • the record of the experience that underlies learning and that influences subsequent processing or behavior Long-Term Memory Systems Long-Term Memory Systems Memory: The Basic Problems Insights into Memory’s Architecture Neural Firing & Hemodynamics Neural Firing & Hemodynamics Imaging Memory in Humans Hemodynamic measures (indirect) • PET – indexes changes in blood flow correlated w/ neural activity – strengths: can index metabolism and receptor density – limits: radiation; cost; low temporal and spatial resolution • fMRI – indexes changes in blood oxygenation levels correlated w/ activity – strengths: non-invasive; high spatial resolution; individual or group analyses; permits event-related designs – limits: temporal resolution restricted by hemodynamic response PET PET Signal is always RELATIVE fMRI Signal Contrast fMRI Blood Oxygen Level Dependent Contrast BOLD fMRI Signal fMRI Studies of Cognition Neuroimaging Approaches Binary comparisons • full- vs. divided-attention during episodic encoding (e.g., Shallice et al., 1994) • “deep” vs. “shallow” processing during episodic encoding (e.g., Kapur et al., 1994) • phonological store and rehearsal vs. rehearsal (e.g., Paulesu et al., 1993) Subtractive / Hierarchical Logic Neuroimaging Approaches: Subtractive Logic Issues to consider • subtractive logic -- assumption of “pure insertion” – requires well-designed paradigms and correct task analyses – assumes processes do not interact Parametric Designs Systematically vary the levels of one factor • e.g., varying working memory load (e.g., Braver et al., 1997) Conjunctive Logic Conduct multiple contrasts, each thought to share a common processing difference Blocked fMRI Designs Event-Related fMRI Response to Averaged Single Trials Variance Associated with Fixed Interval Designs Variance Associated with Jittered Designs Shorter Lags Yield Greater Neural Priming Neural Regions Predicting Subsequent Memory Choosing Your Design Event-related designs • minimize set effects (although state can effects still remain) • permit subject-determined analysis, including parametric analysis • provide an index of the task-elicited hemodynamic response – provides some limited temporal information (time to onset and time to peak) Limitations of ER-fMRI • task/process “impurity” • lower statistical power What does neuroimaging tell us? Function-structure relations Dissociative data to test cognitive and neural theories Functional co-localization = novel process insights What does neuroimaging tell us? Correlational data -- does not address necessity – e.g., delay conditioning and MTL (Blaxton et al., 1996)