Performance of individuals with left hemisphere stroke and aphasia and individuals with right brain damage on forward and backward digit span tasks

Background: Working memory (WM) limitations have been suggested as a significant source of the linguistic processing deficits observed in individuals with aphasia (IWA). Digits forward (DF) and digits backward (DB) span tasks are frequently used to study WM in both healthy and clinical populations. Unfortunately only a handful of studies have explored digit span in IWA.

Aims: The purpose of the current study is to measure the DF and DB spans of IWA and compare their digit spans to a group with right brain damage, but no aphasia (RBD). Additionally, DF and DB span is compared within each group to determine if there is indeed a performance differential that may support the idea that DB is a more difficult WM task in these populations.

Methods & Procedures: A total of 17 IWA and 14 individuals with RBD participated in a DF and DB span task. Modifications to the span tasks were implemented to accommodate language deficits. A series of two digits were orally presented to each participant continuing to a maximum of eight digits. There were seven trials per digit series. Participants were asked to point to the correct order of digits on a written one- to nine-digit list provided on individual note cards or to verbally repeat the numbers if the participant was able to do so.

Outcomes & Results: IWA demonstrated shorter digit spans than the RBD group. Both groups performed worse on the DB span tasks than the DF span tasks.

Conclusions: The results are consistent with previous studies suggesting that DB span is shorter than DF span in other populations and that there are differences in performance on digit span tasks between the two groups. The differences between RBD group and IWA may be explained by decreased attentional capacity or inefficient resource allocation in IWA, or alternatively, a deficient phonological loop. Future studies should explore these possibilities.     

Positive effects of a computerised working memory and executive function training on sentence comprehension in aphasia

Aphasia, the language disorder following brain damage, is frequently accompanied by deficits of working memory (WM) and executive functions (EFs). Recent studies suggest that WM, together with certain EFs, can play a role in sentence comprehension in individuals with aphasia (IWA), and that WM can be enhanced with intensive practice. Our aim was to investigate whether a combined WM and EF training improves the understanding of spoken sentences in IWA. We used a pre–post-test case control design. Three individuals with chronic aphasia practised an adaptive training task (a modified n-back task) three to four times a week for a month. Their performance was assessed before and after the training on outcome measures related to WM and spoken sentence comprehension. One participant showed significant improvement on the training task, another showed a tendency for improvement, and both of them improved significantly in spoken sentence comprehension. The third participant did not improve on the training task, however, she showed improvement on one measure of spoken sentence comprehension. Compared to controls, two individuals improved at least in one condition of the WM outcome measures. Thus, our results suggest that a combined WM and EF training can be beneficial for IWA.     

Validity of an eye-tracking method to index working memory in people with and without aphasia

Background: Working memory (WM) is essential to auditory comprehension; thus understanding of the nature of WM is vital to research and clinical practice to support people with aphasia. A key challenge in assessing WM in people with aphasia is related to the myriad deficits prevalent in aphasia, including deficits in attention, hearing, vision, speech, and motor control of the limbs. Eye-tracking methods augur well for developing alternative WM tasks and measures in that they enable researchers to address many of the potential confounds inherent in tasks traditionally used to study WM. Additionally, eye-tracking tasks allow investigation of trade-off patterns between storage and processing in complex span tasks, and provide on-line response measures.

Aims: The goal of the study was to establish concurrent and discriminative validity of a novel eye movement WM task in individuals with and without aphasia. Additionally we aimed to explore the relationship between WM and general language measures, and determine whether trade-off between storage and processing is captured via eye-tracking measures.

Methods & Procedures: Participants with (n?=?28) and without (n?=?32) aphasia completed a novel eye movement WM task. This task, incorporating natural response requirements, was designed to circumvent potential confounds due to concomitant speech, motor, and attention deficits. The task consisted of a verbal processing component intermixed with presentation of colours and symbols for later recall. Performance on this task was indexed solely via eye movements. Additionally, participants completed a modified listening span task that served to establish concurrent validity of the eye-tracking WM task.

Outcomes & Results: Performance measures of the novel eye movement WM task demonstrated concurrent validity with another established measure of WM capacity: the modified listening span task. Performance on the eye-tracking task discriminated effectively between participants with and without aphasia. No consistent relationship was observed between WM scores and Western Aphasia Battery aphasia quotient and subtest scores for people with aphasia. Additionally, eye-tracking measures yielded no trade-off between processing and storage for either group of participants.

Conclusions: Results support the feasibility and validity of employing a novel eye-tracking method to index WM capacity in participants with and without aphasia. Further research is required to determine the nature of the relationship between WM, as indexed through this method, and specific aspects of language impairments in aphasia.     

Coping resources in individuals with aphasia

Background: Individuals with aphasia (IWA) may be under considerable stress due to the nature of language impairments and other stroke sequelae. IWA have reported a greater perception of stress compared to neurologically intact individuals, including fewer perceived coping resources to assuage the effects of this stress.

Aims: This study sought to identify which areas of coping resources are perceived to be available or unavailable to IWA in comparison with those with right brain damage (RBD) and neurologically intact individuals.

Methods & Procedures: A total of 31 IWA, 12 individuals with RBD, and 14 neurologically intact individuals completed the Coping Resources Inventory for Stress with a caregiver, spouse, or friend to facilitate comprehension of test items. Subtest scores were compared for group differences.

Outcomes & Results: All three groups perceived similar coping resources in the areas of social support and financial freedom. IWA perceived fewer resources than those with RBD and neurologically intact individuals in the areas of stress monitoring and tension control. Both IWA and those with RBD perceived fewer resources in the area of acceptance.

Conclusions: IWA have retained coping resources in some areas, specifically confidence, social support and financial freedom. Helping IWA use these resources may be an effective way to reduce stress in this population. IWA may also benefit from counselling in coping resources, specifically in the areas of stress monitoring and tension control. Counselling programmes should educate IWA on the chronic nature of aphasia and how acceptance may be a useful coping resource in later stages of recovery.     

A cross-language study of verbal and visuospatial working memory span

This cross-language study of working memory compared 30 English speakers and 30 Mandarin Chinese speakers on backward and forward digit and spatial span. Mandarin speakers had greater spans on forward digit and spatial span than did English speakers. Effects were most significant for digit span where the mean score of the English speakers was equivalent to the lowest individual score from Mandarin speakers. Shorter articulation time for digits in spoken Mandarin may account for higher digit spans than those observed in English. The current study indicates that clinical applications of working memory tests should consider cross-language effects, particularly in the evaluation of verbal working memory deficits.     

Short-term memory treatment: patterns of learning and generalisation to sentence comprehension in a person with aphasia

Auditory-verbal short-term memory deficits (STM) are prevalent in aphasia and can contribute to sentence comprehension deficits. This study investigated the effectiveness of a novel STM treatment in improving STM (measured with span tasks) and sentence comprehension (measured with the Token Test and the Test for the Reception of Grammar, TROG) in a person with severe aphasia (transcortical motor). In particular, the research questions were: (1) Would STM training improve STM? (2) Would improvements from the STM training generalise to improvements in comprehension of sentences? STM was trained using listening span tasks of serial word recognition. No other language or sentence comprehension skills were trained. Following treatment, STM abilities improved (listening span, forward digit span). There was also evidence of generalisation to untreated sentence comprehension (only on the TROG). Backward digit span, phonological processing and single word comprehension did not improve. Improvements in sentence comprehension may have resulted from resilience to rapid decay of linguistic representations within sentences (words and phrases). This in turn facilitated comprehension.     

Direct and indirect treatment approaches for addressing short-term or working memory deficits in aphasia

Background: A growing literature has documented that aphasia is frequently accompanied by deficits of short-term memory (STM) and working memory (WM), and that such memory impairments may negatively influence language abilities and aphasia treatment outcomes. Consequently, treating STM and WM impairments in individuals with aphasia should not only remediate these memory impairments but also positively affect their response to language therapy programmes.

Aims: This paper critically reviews the aphasia literature pertaining to remediating, directly or indirectly, STM and WM deficits. Memory treatment protocols developed for other disordered as well as healthy populations are also discussed as possible therapy approaches to consider in future aphasia research.

Main Contribution: Findings from a limited set of studies suggest that STM and WM impairments in individuals with aphasia do respond to treatment, and further that these treatments may also positively affect the language abilities of individuals with aphasia.

Conclusions: Further research is warranted to establish the reliability and validity of these preliminary findings and to explore application of these treatments as well as those developed for nonaphasic populations to individuals representing a broader spectrum of aphasia types and severities.     

Digit repetition performance in patients with focal brain damage

Digit span forward and backward was investigated in well-matched samples of patients with discrete quadrant brain lesions. The incidence of significantly impaired digit repetition performance and the incidence of large forward and backward digit span discrepancies were also studied. Correlational data of digit span performance and various intellectual, memory, and constructional measures was examined. Approximately 60% of all brain-damaged patients showed an impairment of digit span forward, while only 5% showed a similar impairment on the digit span backward task. These data indicate that digit span forward is a more sensitive measure of brain dysfunction from focal brain lesions. No difference was found in the performance of patients with right or left hemisphere lesions; however, the low incidence of aphasia (8%) in this sample may account in part for the relatively adequate performance by the left hemisphere patients. Although the current data regarding visual constructive deficits and impaired ability to repeat digits backward is inconclusive, there did not appear to be a strong relationship between these two functions for these patients. Digit repetition performance does appear to be related to both general intellectual ability and to performance on the Wechsler Memory Scale.     

Phonological short-term memory in conduction aphasia

Background: Within cognitive neuropsychological models conduction aphasia has been conceptualised as a phonological buffer deficit. It may affect the output buffer, the input buffer, or both. The phonological output buffer is a short-term storage, responsible for the short-term maintenance of phonological units until their articulation, as well as for phonological and morphological composition. The phonological input buffer holds input strings until they are identified in the input lexicon. Thus the phonological buffers are closely related to phonological short-term memory (pSTM), and hence it is important to assess pSTM in conduction aphasia. Because the input and output buffers play different roles, impairment in each of them predicts different impairments in the patient's ability to understand certain sentences, to learn new words and names, and to remember and recall lists of words and numbers for short time periods.

Aims: This study explored in detail pSTM in individuals with conduction aphasia, comparing individuals with input and output deficits, recall and recognition tasks, and stimuli of various types. It also tested pSTM in six age groups of healthy individuals, assessing the effect of age on various types of stimuli. This paper presents a new battery of 10 recall and recognition span tests, designed to assess pSTM in aphasia and to measure spans and effects on spans.

Methods & Procedures: The participants were 14 Hebrew-speaking individuals with conduction aphasia, 12 with input or input-output phonological buffer deficit, and 2 with only output deficit, and 296 healthy individuals.

Outcomes & Results: The analyses of the spans and effects on pSTM in the 10 tests indicated that all the participants with conduction aphasia had limited pSTM, significantly poorer than that of the control participants, and no semantic STM impairment. They had shorter spans, smaller length and similarity effects, and larger sentential effect than the controls. The individuals with conduction aphasia who had an impairment in the phonological input buffer showed deficit in both the recall and recognition span tasks. The individuals with the output conduction aphasia showed impairment only in the recall tasks. The healthy individuals showed age effect on span tasks involving words, but no effect of age on span tasks of nonwords.

Conclusions: pSTM is impaired in conduction aphasia, and different pSTM impairments characterise different types of conduction aphasia. Output conduction aphasia causes difficulties only when verbal output is required, whereas input conduction aphasia also causes a deficit when only recognition is required. This suggests that rehearsal can take place without the phonological output buffer. Age differentially affects pSTM for words and nonwords in healthy adults: whereas the encoding of words changes, the ability to remember nonwords is unchanged.     

Relation of forward and backward digit repetition to neurological impairment in children with learning disabilities

The WISC digit span scaled scores of 297 children with learning disabilities fell below any of their overall I.Q. measures. More than 30 per cent of these Ss also had a greater than normal difference of 3 or more digits between their forward and backward spans. When 292 Ss for whom neurological data were available were categorized according to their signs (none, predominantly left, right, or bilateral), Ss with right-sided signs (presumed left hemisphere damage) were worse on digits forward, while Ss with left-sided signs (presumed right hemisphere damage) were worse on digits backward. Most Ss who could not repeat digits backward at all had bilateral impairment.Analysis of the data by age, suggests that the large gap between forward and backward digits, characteristic of the group with left-sided signs, tends to increase with age since their ability to repeat digits forward improves without concommitant improvement in their ability to repeat them backward. Conversely, the backward span of the group with right-sided signs tends to “catch up” and even equal their limited forward repetition.The data appear to support a left-hemisphere-dependent auditory verbal component of the digit span task reflected in digits forward and a right-hemisphere-dependent, visuo-spatial component reflected in digits backward. The distribution of verbal and performance WISC scores of these Ss, as well as their forward and backward digit spans, suggest that patterns of adult hemispheric asymmetry are similar in children with restricted early brain damage.     

Short term memory and working memory in blind versus sighted children

There is evidence that blind people may strengthen their memory skills to compensate for absence of vision. However, which aspects of memory are involved is open to debate and a developmental perspective is generally lacking. In the present study, we compared the short term memory (STM) and working memory (WM) of 10-year-old blind children and sighted children. STM was measured using digit span forward, name learning, and word span tasks; WM was measured using listening span and digit span backward tasks. The blind children outperformed their sighted peers on both STM and WM tasks. The enhanced capacity of the blind children on digit span and other STM tasks confirms the results of earlier research; the significantly better performance of the blind children relative to their sighted peers on verbal WM tasks is a new interesting finding. Task characteristics, including the verbal nature of the WM tasks and strategies used to perform these tasks, are discussed.     

Shared and distinct neurophysiological components of the digits forward and backward tasks as revealed by functional neuroimaging

The digits forward (DF) and backward (DB) tasks are widely used neuropsychological measures believed to tap overlapping systems of phonological processing and working memory. Studies of focal brain lesions have partially elucidated the brain regions essential for these tasks; however relatively little information exists on the underlying functional neuroanatomy in the intact brain. We therefore examined the shared and separate neural systems of these tasks in two positron emission tomography (PET) experiments. In Experiment 1, eight healthy participants performed verbal DF, DB, and a sensorimotor control task during measurement of regional cerebral blood flow (rCBF). DF and DB each activated frontal, parietal, and cerebellar regions as well as prominently activating medial occipital cortex. To eliminate possible visuospatial confounds, Experiment 2 replicated the first experiment in six additional healthy participants who were blindfolded during the study. No differences in activation were found between the two experimental groups. Combined data from both experiments demonstrate that DF and DB rely upon a largely overlapping functional neural system associated with working memory, most notably right dorsolateral prefrontal cortex (DLPFC) and bilateral inferior parietal lobule (IPL) as well as the anterior cingulate, a region associated with attentional effort. The degree of activation increased linearly with increasing task difficulty in DF. DB additionally recruited bilateral DLPFC, left IPL, and Broca's area. Medial occipital cortex (including higher and lower visual processing areas) was robustly activated in both DF and DB and could not be attributed to visual processing per se, suggesting a possible visual imagery strategy for these aural-verbal tasks.     

The contribution of working memory to language comprehension: differential effect of aphasia type

Background: Experimental studies of short-term memory and working memory (WM) in aphasia fail to discriminate cognitive impairments of different aphasia types—non-fluent, Broca-type aphasia and fluent, Wernicke-type aphasia. However, based on the varying fundamental features of these two aphasia syndromes, the potentially different underlying mechanisms of impairment and scant preliminary evidence of varying cognitive deficits, a differential relationship between cognitive function and language processing in these two groups can be predicted.

Aims: The current study investigates the hypothesis concerning the differential impact of cognitive impairments in individuals with fluent versus non-fluent aphasia types.

Methods & Procedures: Participants with fluent (n = 19) and non-fluent (n = 16) aphasia and participants without brain damage (n = 36) were presented with an eye-tracking WM task. Additionally, individuals with aphasia completed two language comprehension tasks.

Outcomes & Results: Results revealed significant decrease in WM capacity in individuals with aphasia compared with participants without brain damage. The two aphasia groups performed similarly on the WM and language tasks. Furthermore, for participants with non-fluent aphasia, it was revealed that WM makes a significant contribution to language comprehension, while for fluent individuals this relationship was not significant.

Conclusions: Overall, the present data support the claim that there are cognitive deficits in aphasia and that these cognitive deficits tend to exacerbate the language impairments of persons with non-fluent aphasia types. The results are discussed in the context of varying mechanisms of impairment in different types of aphasia. The present findings have important implications both for the assessment and the treatment of individuals with aphasia and for understanding the nature of aphasia.     

Age-related working memory decline in patients with Parkinson's disease]

The purpose of this study was to investigate the age-related working memory(WM) decline in patients with Parkinson's disease(PD) using Baddeley's WM model. This model consists of the central executive (CE) and two slave systems, the phonological loop (PL) for the storage of verbal materials, and the visuospatial sketchpad(VSSP) for the storage of visuospatial information. The participants of this study were 22 PD, 11 old (age of 68-78, mean age, 70.5) and age of onset, duration of illness, medication time, and Yahr stage, global cognitive status-matched 11 young(age of 39-58, mean age, 51.5) PD, age- and educational years, global cognitive status-matched 22 normal control (NC), 11 old(age of 65-78, mean age, 70.4) and 11 young(age of 45-57, mean age, 52.4). Mental calculation span of digit sequences, digit forward and backward span, visual memory span were carried out. Age related decline of WM was found in both groups, but processing related differences were revealed between the two groups. NC group showed significant decline with aging in digit backward span. In contrast, in mental calculation span, PD groups showed significant deficit revealed in young PD group and declined significantly with aging and significant decline was not found in digit backward span. In term of the processing and difficulty of WM tasks, digit backward span that needs maintenance of digit sequences and re-ordering, was more difficult than mental calculation that needs maintenance of digit sequences, summation of the digit and updating of the results. There were not significant differences between four groups in digit forward span, visual memory span. The results indicated that the WM span in normal aging declined as task difficulty increased. Their performance decline may be caused by the CE dysfunction. On the other hand, PD showed a characteristic CE deficit observed in mental calculation even in young age and decline with aging. Such decline may be caused by peculiar processing related dysfunction of CE that assumes to be essential deficit of PD.     

Verbal working memory impairment in schizophrenia patients and their first-degree relatives: evidence from the digit span task

OBJECTIVE: The evidence for verbal working memory deficits in schizophrenia has been inconsistent. Few studies have evaluated verbal working memory in the first-degree relatives of schizophrenia patients, who likely share the genetic diathesis for schizophrenia but not the potential confounds associated with chronic mental illness. METHOD: The Wechsler Digit Span Task was used to investigate verbal working memory in 52 schizophrenia patients, 56 of their first-degree relatives, and 73 nonpsychiatric comparison subjects. RESULTS: The nonpsychotic relatives showed no impairment on the forward digit span task, a measure of general attention, but did show impairment on the backward digit span task, a measure of verbal working memory. Schizophrenia patients showed impairment on both the forward and backward digit span tasks. CONCLUSIONS: These results indicate that the forward and backward digit span tasks tap different cognitive abilities that are differentially associated with the diathesis for schizophrenia. Working memory deficits associated with schizophrenia appear to be generalized and not limited to the spatial modality.     

Neural correlates of working memory performance in adolescents and young adults with dyslexia

Behavioral studies indicate deficits in phonological working memory (WM) and executive functioning in dyslexics. However, little is known about the underlying functional neuroanatomy. In the present study, neural correlates of WM in adolescents and young adults with dyslexia were investigated using event-related functional magnetic resonance imaging (fMRI) and a parametric verbal WM task which required the manipulation of verbal material. Dyslexics were not significantly slower than controls; however, they were less accurate with the highest WM demand. The functional analysis excluded incorrectly performed and omitted trials, thus controlling for potential activation confounds. Compared with control subjects, both increased and decreased activation of the prefrontal cortex were found in the dyslexic group. Dyslexics showed significantly more activation than controls with increasing WM demand in the left superior frontal gyrus (BA 8), as well as in the inferior frontal gyrus including Broca's area (BA 44) and its right homologue. Less activation was found in the middle frontal gyrus (BA 6) and in the superior parietal cortex (BA 7). A positive correlation between activation of prefrontal regions and verbal WM performance (as measured by digit span backwards) was found only in the dyslexic group. Accuracy deficits at the highest cognitive demand during the verbal WM task and the digit span backwards suggest that manipulation rather than maintenance is selectively impaired in dyslexics. The fMRI data provide further evidence for functional differences in cortical regions associated with language processing and executive function in subjects with dyslexia.     

A central executive deficit in patients with Parkinson''s disease.

Eight patients with Parkinson's disease and eight matched controls were tested for concurrent task performance to examine whether Parkinson's disease produces deficits in the coordinating and integrating function of the central executive component of Baddeley's working memory model. Consistent with this prediction, the patients showed a significant decline in performance on a random pursuit tracking task while recalling digit span forward sequences, whereas the controls showed no such change. Performance on the component pursuit and digit span tasks, which did not differ between groups, was equated across subjects by varying the size of a target square and by using individual subjects' digit spans. The patient group also produced poorer word fluency scores and reported higher levels of depression, but there was no significant impairment on the Wisconsin card sort test. There was no association between dual task performance and any psychometric measure, target size, or disease related variables. Baddeley's working memory model is advantageous in providing a rich conceptual basis to explore and characterise cognitive abilities in patients with Parkinson's disease.     

A comparison of two working memory tasks in aphasia

Background: Overall, there is growing consensus that working memory (WM) should be routinely assessed in individuals with aphasia as it can contribute significantly to their level of language impairment and be an important factor in treatment planning. However, there is still no consensus in the field as to which tasks should be used to assess WM in aphasia. The two main alternatives are adapted complex span tasks and N-back tasks. Both have been used interchangeably in previous studies of WM in aphasia, even though the correspondence between the two tasks has not been properly established.

Aims: The current study investigates the relationship between two WM tasks—complex span and N-back tasks—in a large sample of individuals with aphasia. The relationships of these tasks to measures of language comprehension are also explored, as well as differences in performance patterns between individuals with non-fluent and fluent aphasia.

Methods & Resources: Forty-four participants with aphasia (non-fluent: n = 27; fluent: n = 13; mixed: n = 4) were examined with a modified listening span task (Ivanova & Hallowell, 2014), an auditory verbal 2-back task, and a standardised Russian language comprehension test.

Outcomes & Results: Results revealed a moderate relationship between the two WM measures, but demonstrated a divergence in terms of their relationship to language comprehension. Performance on the modified listening span task was related to language comprehension abilities, but performance on the 2-back task was not, suggesting that the two tasks primarily index different underlying cognitive mechanisms. Furthermore, the relationship between the modified listening span task and language comprehension was significant for individuals with non-fluent aphasia, but not for those with fluent aphasia.

Conclusions: Overall, the data demonstrate that while performance of individuals with aphasia was related on the two tasks, the two tasks cannot be substituted for one another without further inquiries into their underlying differences.     

Forward and backward digit span difficulties in children with specific learning disorder

This study examined performance in the forward and backward digit span task of the Wechsler Intelligence Scale for Children–Fourth Edition (WISC–IV) in a large group of children with specific learning disorder (SLD) as compared with a group of typically developing children matched for age and sex. Our results further support the hypothesis that the intellectual difficulties of children with SLD involve working memory in the forward digit span task to a greater extent than in the backward digit span task. The correlation of the two spans with a General Ability Index (GAI) was similar in SLD, and smaller in magnitude than in typically developing children. Despite a GAI within normal range, children with SLD had difficulty with both digit span tasks, but more so for forward span. This pattern was similar for different SLD profiles with clinical diagnoses of dyslexia and mixed disorder, but the impairments were more severe in the latter. Age differences were also investigated, demonstrating larger span impairment in older children with SLD than in younger.     

Working memory and amnesia: the role of stimulus novelty

Despite the traditional view that damage to the hippocampus and/or surrounding areas of the medial temporal lobe (MTL) does not impair short-term or working memory (WM), recent research has shown MTL amnesics to be impaired on WM tasks that require maintaining a small amount of information over brief retention intervals (e.g., maintenance of a single face for one second). However, the types of tasks that have demonstrated WM impairments in amnesia tend to have involved novel stimuli. We hypothesized that WM may be impaired in amnesia for tasks that require maintaining novel information, but may be preserved for more familiar material, particularly if the material can be easily rehearsed. To test this hypothesis, patient HC, a 22-year-old developmental amnesic with relatively preserved semantic memory and 20 age and education matched controls performed a delayed match-to-sample task that required maintaining a single famous or non-famous face for 1-8s, digit span and reading span tasks, and a modified Brown-Peterson task that required maintaining a single high- or low-frequency word or a non-word for 4-8s. HC's performance was impaired for non-famous faces but preserved for famous faces, impaired for the reading span task but preserved for digit span, and it was impaired for non-words and unfamiliar low-frequency words but preserved for familiar words. These results support the hypothesis that an intact hippocampus is necessary for maintaining a single novel stimulus in WM. However, stimulus familiarity and rehearsal support WM via cortical regions independent of the MTL.