Explicit Retrieval Tasks Research Articles

Neuroanatomical assessment of the impact of negative emotion on explicit memory in patients with obsessive-compulsive disorder.

The aim of this study was to identify the brain activation patterns associated with emotionally neutral or unpleasant words during explicit memory tasks in patients with obsessive-compulsive disorder (OCD) using a functional MRI. Sixteen patients with OCD (mean age=31.4±10.1 years) and 16 healthy controls (mean age=32.6±5.8 years) who had no history of neurological or psychiatric illness underwent functional MRI examinations on a 3-T Siemens MR Scanner. The stimulation paradigm consisted of five times rest-condition, two times encoding of two-syllable words, and two times explicit retrieval of the previously learned words. Six different words were presented for 3 s each in the encoding and retrieval tasks. In the retrieval task, the same words as those used at the encoding task were presented randomly. Brain activation maps were quantified and analyzed using SPM8 and MRIcron software. During the explicit retrieval tasks with emotionally neutral words, the predominant activation areas observed in patients with OCD included the angular gyrus and the supramarginal gyrus, whereas healthy controls showed significantly higher activity in the postcentral gyrus (P<0.005). During the explicit retrieval tasks with unpleasant words, patients with OCD showed significantly higher activity, compared with healthy controls, in the cerebellum, posterior cingulate gyrus, middle occipital gyrus, middle temporal gyrus, and inferior frontal gyrus (P<0.005); however, no predominant activation areas in healthy controls over patients with OCD were observed. This study showed differential brain activation patterns in response to emotionally neutral and unpleasant words in patients with OCD. This finding will be useful in assessing the neural mechanisms associated with emotional effect on the impairment of memory retrieval in OCD.

Role of the Frontal Lobes in Implicit and Explicit Retrieval Tasks

While the role of the frontal lobes in explicit retrieval tasks is well supported, the findings for implicit tasks are less conclusive. We investigated the role of the frontal lobes in perceptual and conceptual implicit priming. Three memory paradigms were given under both implicit and explicit retrieval instructions, using word fragment completion, picture fragment completion and category exemplar generation. Three groups of individuals with frontal lesions were compared to normal controls: Left dorsolateral lesions (n = 5), right dorsolateral lesions (n = 4), and medial lesions (n = 9). Word fragment completion priming was impaired by left dorsolateral lesions, with other priming tests unaffected by any lesion. Explicit performance showed a different pattern, with category exemplar cued recall impaired by left dorsolateral and medial lesions. These findings support the role of the frontal lobes in both implicit and explicit retrieval mechanisms under certain conditions requiring strategy application or lexical retrieval.

Neural Mechanism of Implicit and Explicit Memory Retrieval: Functional MR Imaging

Purpose: To identify, using functional MR imaging, distinct cerebral centers and to evaluate the neural mechanism associated with implicit and explicit retrieval of words during conceptual processing. Materials and Methods: Seven healthy volunteers aged 21-25 (mean, 22) years underwent BOLD-based fMR imaging using a 1.5T Signa Horizon Echospeed MR system. To activate the cerebral cortices, a series of tasks was performed as follows: the encoding of two-syllable words, and implicit and explicit retrieval of previously learned words during conceptual processing. The activation paradigm consisted of a cycle of alternating periods of 30 seconds of stimulation and 30 seconds of rest. Stimulation was accomplished by encoding eight twosyllable words and the retrieval of previously presented words, while the control condition was a white screen with a small fixed cross. During the tasks we acquired ten slices (6 mm slice thickness, 1 mm gap) parallel to the AC-PC line, and the resulting functional activation maps were reconstructed using a statistical parametric mapping program (SPM 99). Results: A comparison of activation ratios (percentages), based on the number of volunteers, showed that activation of Rhs-35, PoCiG-23 and ICiG-2630 was associated with explicit retrieval only; other brain areas were activated during the performance of both implicit and explicit retrieval tasks. Activation ratios were higher for explicit tasks than for implicit; in the cingulate gyrus and temporal lobe they were 30% and 10% greater, respectively. During explicit retrieval, a distinct brain activation index (percentage) was seen in the temporal, parietal, and occipital lobe and cingulate gyrus, and PrCeG-4, Pr/PoCeG-43 in the frontal lobe. During implicit retrieval, on the other hand, activity was greater in the frontal lobe, including the areas of SCA-25, SFG/MFG-10, IFG-4445, OrbG-1147, SFG-68, and MFG-946. Overall, activation was lateralized mainly in the left hemisphere during both implicit and explicit retrieval tasks. For explicit retrieval, the lateralization index was more than twice as high as for implicit retrieval. Conclusion: Our findings indicate that there is neuro-anatomical dissociation between implicit and explicit retrieval of words during conceptual processing, suggesting, on the basis of cognitive neuroscience, that the performance of implicit and explicit memory-related tasks involves different mechanisms.

Building episodic connections: Changes in episodic priming with age and dementia.

Previous studies of associative encoding that used explicit retrieval tasks have shown both age- and dementia of the Alzheimer type (DAT)-related declines, but such results may be biased by group differences in explicit retrieval. In the present experiment, the authors assessed implicit associative encoding for 25 younger adults (ages 18-25), 73 healthy older adults (ages 59-91), and 65 adults with DAT (ages 59-91) during a speeded word-naming task using an episodic priming measure. Episodic priming refers to the facilitation in responding to a target word after repetition of both words in a prime-target pair, in comparison with simple repetition of the target word with a new prime on each presentation. In contrast with other studies of implicit associative encoding that did not use an implicit episodic priming measure, the present study found both age- and DAT-related declines in associative encoding under conditions of massed learning trials.

Effects of attentive encoding on analytic and nonanalytic processing in implicit and explicit retrieval tasks

The least-frequent meanings of homophones were biased by two exposure conditions that varied in the extent to which the processing of biasing information was attentive and effortful. Memory was assessed with both explicit (recognition) and implicit tasks. For the implicit task, scores reflected the extent to which the biased meanings were apparent in subjects’ later spellings of or free associatons to old homophones. The results indicate that attentive processing during encoding is likely to invite analytic processing in both implicit and explicit tasks. Furthermore, unattended exposure may lead to nonanalytic processing across both tasks, with subjects relying on a fluency heuristic for the explicit task. Comparable results were obtained from the spelling and the free-association tasks.