Comparative electrophysiological and hemodynamic measures of neural activation during memory‐retrieval
Bibliographic record
Abstract
The spatial and temporal characteristics of the brain processes underlying memory retrieval were studied with both event-related potentials (ERP) and positron emission tomography (PET) techniques. Subjects studied lists of 20 words and then performed episodic (old/new judgment) or semantic (living/nonliving decision) retrieval tasks on multiple four-item test lists, each lasting 10 sec. The PET and ERP measurements at test were assessed in relation to both the task (episodic vs. semantic) and the item (old vs. new or living vs. nonliving). Episodic retrieval was associated with increased blood flow in the right frontal lobe (Brodmann Area 10) and a sustained, slowly developing positive ERP shift recorded from the right frontopolar scalp. Semantic retrieval was associated with increased blood flow in the left frontal (Area 45) and temporal (Area 21) lobes but no clear ERP concomitant. The two retrieval tasks also differed from each other in the ERPs to single items in an early (300-500 ms) time window. Item-related comparisons yielded convergent results mainly if the retrieved information was relevant to the given task (e.g., old/new items during episodic retrieval and living/nonliving items during semantic retrieval). Episodically retrieved old items were associated with increased blood flow in the left medial temporal lobe and a transient increase in the amplitude of the late positive component (500-700 ms) of the ERP. Semantically retrieved living items were associated with increased blood flow in the left frontal cortex and anterior cingulate and a transient late frontal slow wave (700-1,500 ms) in the ERPs. These results indicate that the brain regions engaged in memory retrieval are active in either a sustained or transient manner. They map task-related processes to sustained and item-related processes to transient neural activity. But they also suggest that task-related factors can transiently affect early stages of item processing.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".