Free Recall Of Word Lists Research Articles

The precuneus as a central node in declarative memory retrieval.

Both, the hippocampal formation and the neocortex are contributing to declarative memory, but their functional specialization remains unclear. We investigated the differential contribution of both memory systems during free recall of word lists. In total, 21 women and 17 men studied the same list but with the help of different encoding associations. Participants associated the words either sequentially with the previous word on the list, with spatial locations on a well-known path, or with unique autobiographical events. After intensive rehearsal, subjects recalled the words during functional magnetic resonance imaging (fMRI). Common activity to all three types of encoding associations was identified in the posterior parietal cortex, in particular in the precuneus. Additionally, when associating spatial or autobiographical material, retrosplenial cortex activity was elicited during word list recall, while hippocampal activity emerged only for autobiographically associated words. These findings support a general, critical function of the precuneus in episodic memory storage and retrieval. The encoding-retrieval repetitions during learning seem to have accelerated hippocampus-independence and lead to direct neocortical integration in the sequentially associated and spatially associated word list tasks. During recall of words associated with autobiographical memories, the hippocampus might add spatiotemporal information supporting detailed scenic and contextual memories.

Age-Related Deficits in Memory Encoding and Retrieval in Word List Free Recall.

Although ageing is known to affect memory, the precise nature of its effect on retrieval and encoding processes is not well understood. Here, we examine the effect of ageing on the free recall of word lists, in which the semantic structure of word sequences was manipulated from unrelated words to pairs of associated words with various separations (between pair members) within the sequence. We find that ageing is associated with reduced total recall, especially for sequences with associated words. Furthermore, we find that the degree of semantic clustering (controlled for chance clustering) shows an age effect and that it interacts with the distance between the words within a pair. The results are consistent with the view that age effects in memory are mediated both by retrieval and by encoding processes associated with frontal control and working memory.

Organizational Strategies Partially Account for Race-related Differences in List Recall Performance.

Organizational strategies have been shown to improve one's ability to recall items from a list. Specifically, use of semantic clustering, the tendency to group items by category when recalling them, predicts better free recall of word lists after short and long delays. The present study utilized a healthy adult sample to examine use of efficient memory strategies as a predictor of differences in neurocognitive findings between African American and white participants. Participants provided demographic information and completed the California Verbal Learning Test-Second Edition (CVLT-II) and Wechsler Abbreviated Scale of Intelligence-Second Edition (WASI-2). Groups were matched across socioeconomic status and years of education. White participants used more semantic clustering and performed better on recall measures after short and long delays than their African American peers, and semantic clustering predicted recall in both groups. Regression analyses suggested that use of semantic clustering is a significant partial mediator of the relationship between race and free recall abilities. Intelligence scores from the WASI-2 were correlated with CVLT-II measures in white participants but not African American participants. Despite quantitatively similar backgrounds, white and African American participants differed in recall performance. However, this study showed that African American participants' poorer recall may be partially attributed to less frequent use of semantic clustering as a strategy. These discrepancies may be rooted in inequalities in educational experiences and suggest that providing organizational strategies during early learning may be an area of intervention to mitigate racial differences seen in neuropsychological testing.

A Spiking Working Memory Model Based on Hebbian Short-Term Potentiation

A dominant theory of working memory (WM), referred to as the persistent activity hypothesis, holds that recurrently connected neural networks, presumably located in the prefrontal cortex, encode and maintain WM memory items through sustained elevated activity. Reexamination of experimental data has shown that prefrontal cortex activity in single units during delay periods is much more variable than predicted by such a theory and associated computational models. Alternative models of WM maintenance based on synaptic plasticity, such as short-term nonassociative (non-Hebbian) synaptic facilitation, have been suggested but cannot account for encoding of novel associations. Here we test the hypothesis that a recently identified fast-expressing form of Hebbian synaptic plasticity (associative short-term potentiation) is a possible mechanism for WM encoding and maintenance. Our simulations using a spiking neural network model of cortex reproduce a range of cognitive memory effects in the classical multi-item WM task of encoding and immediate free recall of word lists. Memory reactivation in the model occurs in discrete oscillatory bursts rather than as sustained activity. We relate dynamic network activity as well as key synaptic characteristics to electrophysiological measurements. Our findings support the hypothesis that fast Hebbian short-term potentiation is a key WM mechanism. <b>SIGNIFICANCE STATEMENT</b> Working memory (WM) is a key component of cognition. Hypotheses about the neural mechanism behind WM are currently under revision. Reflecting recent findings of fast Hebbian synaptic plasticity in cortex, we test whether a cortical spiking neural network model with such a mechanism can learn a multi-item WM task (word list learning). We show that our model can reproduce human cognitive phenomena and achieve comparable memory performance in both free and cued recall while being simultaneously compatible with experimental data on structure, connectivity, and neurophysiology of the underlying cortical tissue. These findings are directly relevant to the ongoing paradigm shift in the WM field.

A Spiking Working Memory Model Based on Hebbian Short-Term Potentiation

A dominant theory of working memory (WM), referred to as the persistent activity hypothesis, holds that recurrently connected neural networks, presumably located in the prefrontal cortex, encode and maintain WM memory items through sustained elevated activity. Reexamination of experimental data has shown that prefrontal cortex activity in single units during delay periods is much more variable than predicted by such a theory and associated computational models. Alternative models of WM maintenance based on synaptic plasticity, such as short-term nonassociative (non-Hebbian) synaptic facilitation, have been suggested but cannot account for encoding of novel associations. Here we test the hypothesis that a recently identified fast-expressing form of Hebbian synaptic plasticity (associative short-term potentiation) is a possible mechanism for WM encoding and maintenance. Our simulations using a spiking neural network model of cortex reproduce a range of cognitive memory effects in the classical multi-item WM task of encoding and immediate free recall of word lists. Memory reactivation in the model occurs in discrete oscillatory bursts rather than as sustained activity. We relate dynamic network activity as well as key synaptic characteristics to electrophysiological measurements. Our findings support the hypothesis that fast Hebbian short-term potentiation is a key WM mechanism.SIGNIFICANCE STATEMENT Working memory (WM) is a key component of cognition. Hypotheses about the neural mechanism behind WM are currently under revision. Reflecting recent findings of fast Hebbian synaptic plasticity in cortex, we test whether a cortical spiking neural network model with such a mechanism can learn a multi-item WM task (word list learning). We show that our model can reproduce human cognitive phenomena and achieve comparable memory performance in both free and cued recall while being simultaneously compatible with experimental data on structure, connectivity, and neurophysiology of the underlying cortical tissue. These findings are directly relevant to the ongoing paradigm shift in the WM field.

Inert gas narcosis disrupts encoding but not retrieval of long term memory

Exposure to increased ambient pressure causes inert gas narcosis of which one symptom is long-term memory (LTM) impairment. Narcosis is posited to impair LTM by disrupting information encoding, retrieval (self-guided search), or both. The effect of narcosis on the encoding and retrieval of LTM was investigated by testing the effect of learning–recall pressure and levels of processing (LoP) on the free-recall of word lists in divers underwater. All participants (n=60) took part in four conditions in which words were learnt and then recalled at either low pressure (1.4–1.9atm/4–9msw) or high pressure (4.4–5.0atm/34–40msw), as manipulated by changes in depth underwater: low–low (LL), low–high(LH), high–high (HH), and high–low (HL). In addition, participants were assigned to either a deep or shallow processing condition, using LoP methodology. Free-recall memory ability was significantly impaired only when words were initially learned at high pressure (HH & HL conditions). When words were learned at low pressure and then recalled at low pressure (LL condition) or high pressure (LH condition) free-recall was not impaired. Although numerically superior in several conditions, deeper processing failed to significantly improve free-recall ability in any of the learning–recall conditions. This pattern of results support the hypothesis that narcosis disrupts encoding of information into LTM, while retrieval appears to be unaffected. These findings are discussed in relation to similar effects reported by some memory impairing drugs and the practical implications for workers in pressurised environments.

The role of the frontal cortex in memory: an investigation of the Von Restorff effect.

Evidence from neuropsychology and neuroimaging indicate that the pre-frontal cortex (PFC) plays an important role in human memory. Although frontal patients are able to form new memories, these memories appear qualitatively different from those of controls by lacking distinctiveness. Neuroimaging studies of memory indicate activation in the PFC under deep encoding conditions, and under conditions of semantic elaboration. Based on these results, we hypothesize that the PFC enhances memory by extracting differences and commonalities in the studied material. To test this hypothesis, we carried out an experimental investigation to test the relationship between the PFC-dependent factors and semantic factors associated with common and specific features of words. These experiments were performed using Free-Recall of word lists with healthy adults, exploiting the correlation between PFC function and fluid intelligence. As predicted, a correlation was found between fluid intelligence and the Von-Restorff effect (better memory for semantic isolates, e.g., isolate “cat” within category members of “fruit”). Moreover, memory for the semantic isolate was found to depend on the isolate's serial position. The isolate item tends to be recalled first, in comparison to non-isolates, suggesting that the process interacts with short term memory. These results are captured within a computational model of free recall, which includes a PFC mechanism that is sensitive to both commonality and distinctiveness, sustaining a trade-off between the two.

Napping to renew learning capacity: enhanced encoding after stimulation of sleep slow oscillations

As well as consolidating memory, sleep has been proposed to serve a second important function for memory, i.e. to free capacities for the learning of new information during succeeding wakefulness. The slow wave activity (SWA) that is a hallmark of slow wave sleep could be involved in both functions. Here, we aimed to demonstrate a causative role for SWA in enhancing the capacity for encoding of information during subsequent wakefulness, using transcranial slow oscillation stimulation (tSOS) oscillating at 0.75Hz to induce SWA in healthy humans during an afternoon nap. Encoding following the nap was tested for hippocampus-dependent declarative materials (pictures, word pairs, and word lists) and procedural skills (finger sequence tapping). As compared with a sham stimulation control condition, tSOS during the nap enhanced SWA and significantly improved subsequent encoding on all three declarative tasks (picture recognition, cued recall of word pairs, and free recall of word lists), whereas procedural finger sequence tapping skill was not affected. Our results indicate that sleep SWA enhances the capacity for encoding of declarative materials, possibly by down-scaling hippocampal synaptic networks that were potentiated towards saturation during the preceding period of wakefulness.

Free Recall of Word Lists under Total Sleep Deprivation and after Recovery Sleep

One task that has been used to assess memory effects of prior total sleep deprivation (TSD) is the immediate free recall of word lists; however, results have been mixed. A possible explanation for this is task impurity, since recall of words from different serial positions reflects use of distinct types of memory (last words: short-term memory; first and intermediate words: episodic memory). Here we studied the effects of 2 nights of TSD on immediate free recall of semantically unrelated word lists considering the serial position curve. Random allocation to a 2-night TSD protocol followed by one night of recovery sleep or to a control group. Study conducted under continuous behavioral monitoring. 24 young, healthy male volunteers. 2 nights of total sleep deprivation (TSD) and one night of recovery sleep. Participants were shown five 15 unrelated word-lists at baseline, after one and 2 nights of TSD, and after one night of recovery sleep. We also investigated the development of recall strategies (learning) and susceptibility to interference from previous lists. No free recall impairment occurred during TSD, irrespective of serial position. Interference was unchanged. Both groups developed recall strategies, but task learning occurred earlier in controls and was evident in the TSD group only after sleep recovery. Prior TSD spared episodic memory, short-term phonological memory, and interference, allowed the development of recall strategies, but may have decreased the advantage of using these strategies, which returned to normal after recovery sleep.

Effects of degraded sensory input on memory for speech: Behavioral data and a test of biologically constrained computational models

Poor hearing acuity reduces memory for spoken words, even when the words are presented with enough clarity for correct recognition. An “effortful hypothesis” suggests that the perceptual effort needed for recognition draws from resources that would otherwise be available for encoding the word in memory. To assess this hypothesis, we conducted a behavioral task requiring immediate free recall of word-lists, some of which contained an acoustically masked word that was just above perceptual threshold. Results show that masking a word reduces the recall of that word and words prior to it, as well as weakening the linking associations between the masked and prior words. In contrast, recall probabilities of words following the masked word are not affected. To account for this effect we conducted computational simulations testing two classes of models: Associative Linking Models and Short-Term Memory Buffer Models. Only a model that integrated both contextual linking and buffer components matched all of the effects of masking observed in our behavioral data. In this Linking-Buffer Model, the masked word disrupts a short-term memory buffer, causing associative links of words in the buffer to be weakened, affecting memory for the masked word and the word prior to it, while allowing links of words following the masked word to be spared. We suggest that these data account for the so-called “effortful hypothesis”, where distorted input has a detrimental impact on prior information stored in short-term memory.

Memory Enhancement from Two Weeks’ Exposure to North American Ginseng Extract HT1001 in Young and Middle Aged Healthy Adults

In vivo, in vitro, and animal learning studies have reported neuroactive effects of Rb1 and Rg1 ginsenosides that may be relevant to human learning and memory. The objective of this study was to assess potential learning and memory benefits of HT1001, a standardized proprietary North American ginseng (Panax quinquefolius) extract contain- ing Rb1, Rg1 and other important ginsenosides, in healthy volunteers. Neuropsychological assessments were conducted using the Clinical Memory Scale (CMS), which has two parallel forms for baseline and post-treatment assessments. A young adult sample (YAS, n = 10) and a middle aged sample (MAS, n = 10) completed the CMS at baseline and again af- ter 14 days' exposure to 200mg HT1001 daily. The CMS Memory Quotient (MQ) showed significant main effects of time, with higher CMS-MQ on the second assessment compared to the first, and of age group, with the YAS performing better than the MAS. There was no interaction between time and age group. Secondary analyses indicated benefits for both groups on free recall of word lists, cued recall of word pairs, and recognition of figures, and benefits in the YAS but not the MAS on free recall of pictures. Taken together, the results suggest that memory, as measured with the CMS-MQ, was significantly improved with open-label HT1001. While practise effects cannot be completely ruled out, the results presented here are exciting and timely given our increasingly ageing population, and provide preliminary support for a prospective placebo-controlled examination of HT1001 on learning and memory.

138 FREE RECALL OF WORD LISTS DURING SLEEP DEPRIVATION: FOCUS ON RECALL BASED ON SERIAL POSITION

Objective: Free recall of word lists is a commonly used paradigm to investigate learning during sleep deprivation. Here, we studied whether sleep deprivation alters the pattern of recall based on serial positions of words in word lists, which enables the determination of: a) long-term episodic memory learning, or recall of the first words on the lists (primacy effect); b) shortterm learning, or recall ofwords in the last serial positions (recency effect); c) working memory processes involved in transferring information to and from long-term memory. Method: Twenty-four young, healthy male volunteers were randomly allocated to two groups: total sleep deprivation for 48 h or normal sleep (control group). All volunteers took part in 4 test sessions at: baseline, 24 h, 48 h and 72 h (corresponding to a session after one night of recovery sleep in the sleep-deprived group). Five word-lists were presented per session and immediate serial recall was assessed. Each list was composed of 15 unrelated concrete nouns. Results: The sleep-deprived group, both after 24 and 48 h, recalled fewer words in the serial positions following the primacy portion of the list in comparison to the control group. At 72 h, after one night of recovery sleep in the sleep-deprived group, performance of both groups no longer differed, but recall was larger than at baseline in serial positions between the primacy and recency portions of the list, indicating that both groups benefited from the repeated exposure to the task. Conclusions: One and two nights of sleep deprivation impairs memory for words in the serial positions following the primacy portion of the list, possibly due to an extension of primacy in the control group. Because transfer of information to long-term memory is thought to involve secondary processes of active rehearsal and chunking of word sequences, our data indicates that sleep-deprivation impairs the functioning of the episodic buffer of working memory, which is responsible for these cognitive processes. One night of recovery sleep restores these working memory processes to normal. Financial Support: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-2008/089210) and Associacao Fundo de Incentivo a Psicofarmacologia (AFIP).

139 EFFECTS OF ACUTE ADMINISTRATION OF ZOLPIDEM ON A NON-ASSOCIATIVE MEMORY TASK: OPEN-FIELD HABITUATION

Objective: Free recall of word lists is a commonly used paradigm to investigate learning during sleep deprivation. Here, we studied whether sleep deprivation alters the pattern of recall based on serial positions of words in word lists, which enables the determination of: a) long-term episodic memory learning, or recall of the first words on the lists (primacy effect); b) shortterm learning, or recall ofwords in the last serial positions (recency effect); c) working memory processes involved in transferring information to and from long-term memory. Method: Twenty-four young, healthy male volunteers were randomly allocated to two groups: total sleep deprivation for 48 h or normal sleep (control group). All volunteers took part in 4 test sessions at: baseline, 24 h, 48 h and 72 h (corresponding to a session after one night of recovery sleep in the sleep-deprived group). Five word-lists were presented per session and immediate serial recall was assessed. Each list was composed of 15 unrelated concrete nouns. Results: The sleep-deprived group, both after 24 and 48 h, recalled fewer words in the serial positions following the primacy portion of the list in comparison to the control group. At 72 h, after one night of recovery sleep in the sleep-deprived group, performance of both groups no longer differed, but recall was larger than at baseline in serial positions between the primacy and recency portions of the list, indicating that both groups benefited from the repeated exposure to the task. Conclusions: One and two nights of sleep deprivation impairs memory for words in the serial positions following the primacy portion of the list, possibly due to an extension of primacy in the control group. Because transfer of information to long-term memory is thought to involve secondary processes of active rehearsal and chunking of word sequences, our data indicates that sleep-deprivation impairs the functioning of the episodic buffer of working memory, which is responsible for these cognitive processes. One night of recovery sleep restores these working memory processes to normal. Financial Support: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-2008/089210) and Associacao Fundo de Incentivo a Psicofarmacologia (AFIP).

Effects of a benzodiazepine on free recall of semantically related words

Although it is widely known that benzodiazepines impair episodic memory, few studies have investigated their effects upon specific processes involved in free recall. This study evaluated the acute effects of flunitrazepam (1.0 mg; 1.3 mg) and placebo in healthy volunteers on immediate and delayed free recall of word lists considering serial positions as well as semantic relations between words inserted in the middle of the lists (e.g. milk-cheese-butter). Flunitrazepam promoted a global amnestic effect, impairing recall in all serial positions except the last words (recency effect). Primacy and recency effects were preserved as indexed, respectively, by larger recall of the first and last words in relation to adjacent items. Facilitation in recall of semantically related words was not impaired by the drug when compared to recall in adjacent positions, in spite of a dose-dependent diminution of the number of words recalled also in mid-list positions. Flunitrazepam-induced deficits were interpreted as impairment in the formation of new associations between items, or groups of items in the case of related words, and context.

Gross morphology and morphometric sequelae in the hippocampus, fornix, and corpus callosum of patients with severe non-missile traumatic brain injury without macroscopically detectable lesions: a T1 weighted MRI study

Objective: The gross morphology and morphometry of the hippocampus, fornix, and corpus callosum in patients with severe non-missile traumatic brain injury (nmTBI) without obvious neuroradiological lesions was examined and the...

Memory Performance Used to Detect Radiation Effects on Cognitive Functioning

Although radiotherapy remains a necessary and frequently used treatment for brain tumors, uncertainty remains about the nature and severity of neurocognitive morbidity. We show that verbal-semantic memory (free recall of word list) is sensitive to damaging radiation effects in 20 patients with low-grade, supratentorial, primary brain tumors who received moderate doses of partial-brain irradiation. We previously reported that verbal-semantic memory is dissociated from visual memory (acquisition and recall) during the same phase of radiation effects, indicating that memory is differentially affected by radiation. In this study, we provide evidence of the nature of the iatrogenic radiation effect on memory by testing collateral cognitive functions that might explain the specific memory impairment. We found that the verbal-semantic recall impairment was not associated with impairments in auditory attention, auditory processing speed, auditory-verbal working memory, or in the temporal coding or subjective organization of word-list recall. These findings focus damaging radiation effects on primary retrieval processes, rather than on earlier cognitive processes or executive processes affecting recall. Knowledge of the specific patterns of change in cognition would guide the differential diagnosis and rehabilitation of survivors of brain tumors whose conditions are complicated by tumors with multiple treatments.

Verbal short-term memory deficit in Alzheimer's disease: an examination with the free recall paradigm

To examine the relationship between short-term memory deficit and severity of the dementia in Alzheimer's disease, free recall of word lists was investigated. Twenty-seven patients with diagnosis of probable Alzheimer's disease according to NINCDS ADRDA criteria, and twelve age-matched controls participated in the study. Patients were divided into two subgroups: fourteen mild and thirteen moderate dementia by Clinical Dementia Rating (CDR). To evaluate short-term and long-term memory components separately, two measures were used: recency effect in the serial-position free-recall curve, and intra-trial retention interval developed by Tulving and Colotla (1970). Mildly demented patients showed a long-term memory deficit with almost normal short-term memory, but moderate ones showed an overall reduction in both measures. These results suggest that memory disorder in Alzheimer's disease changes not only quantitatively but also qualitatively with the progress of dementia, and short-term memory is relatively preserved in the early stage of the disease.

Developmental trends in memory and metamemory in children with attention deficit disorder.

Examined the development of memory strategy knowledge and spontaneous use of strategy by 6- to 12-year-old boys with ADD-H. Metamemory knowledge of 12 ADD-H boys, unmedicated for study participation, and 12 matched control Ss was compared using a structured interview. Use of categorization was assessed using free recall of word lists differing in category composition (acoustic vs semantic categories) and list organization (clustered by category vs unclustered). Interview data indicated no difference between groups in development of metamemory knowledge. Analysis of free recall performance showed that ADD-H Ss were less likely than controls to benefit from that knowledge when strategy was less salient and involved effortful reorganization of stimuli (p less than .05). The results were consistent with a production deficiency. Developmental trends and implications for remediation are discussed.

Dose-response analysis of the behavioral effects of diazepam: I. Learning and memory

A total of 120 healthy volunteers were randomly assigned to four treatments (placebo, 0.1, 0.2, and 0.3 mg/kg) and three testing times (7 AM, 1 PM and 7 PM). Immediate and delayed free recall of word lists revealed consistent decreases in performance as oral diazepam dose increased from 0.1, 0.2, to 0.3 mg/kg. Paradoxically, as the dose increased, the number of predrug list words recalled also increased. A serial number-learning task displayed a pattern of delayed improvement of acquisition as the dose increased. Response times in a semantic-categories task were prolonged as the dose increased. Parallel recovery functions were observed for all doses and tasks. Full recovery after a single administration of 0.1, 0.2, and 0.3 mg/kg doses was estimated to occur after 3.5, 4.5, and 5.5 h, respectively. Several analyses were consistent with the view that acquisition and not retrieval was impaired by diazepam. There were no circadian interactions with the effects of the drug.

Primary memory and secondary memory in dementia of the Alzheimer type.

Free recall of word lists was investigated in a sample of 47 patients with dementia of the Alzheimer type (DAT) and 31 normal controls of equivalent age and education. Recall was divided into primary memory (PM) and secondary memory (SM) components based on the number of items intervening between presentation and recall. The findings were as follows: (1) the patients showed a greater deficit on the SM than on the PM measure; (2) there was little evidence of proactive interference in the patient group; (3) the PM and SM measures were independent in the controls but not in the patient group; and, (4) the size of patients' PM deficit increased linearly with increasing items between presentation and attempted recall. These results suggest that the memory disorder of DAT is partially the result of defective PM.