Visual working memory for simple and complex features: an fMRI study

Visual working memory (VWM) allows us to hold visual information briefly in our minds after its disappearance. It is important for bridging the present to the immediate past. Previous neuroscience studies on VWM have shown that several parietal, frontal, and occipitotemporal brain regions subserve this function. Those studies, however, have often focused on VWM for a single property, such as color. Yet, in behavior, the capacity of VWM is sensitive to the complexity of to-be-remembered visual features. How do different brain areas represent VWM for visual features of different complexity and for combination of features? To address this question, we used functional MRI to study the response profile of several brain regions in three VWM tasks. In all tasks, subjects saw 1 to 7 colored polygons and had to remember their color (a simple feature), shape (a complex feature), or both color and shape. Behavioral performance showed that VWM reached capacity limit at about 3 colors, 2 shapes, and 2 compound objects. In the fMRI data, we found different functional profiles for frontal, parietal, and occipitotemporal regions. Specifically, the posterior parietal cortex was sensitive to both featural and VWM load manipulations. The prefrontal regions were sensitive to VWM load manipulation but relatively insensitive to featural differences. The occipitotemporal regions were sensitive to featural differences, but not to VWM load manipulation. We propose that the response properties of these regions can jointly account for several findings in human VWM behavior.     

内容记忆和来源记忆的功能磁共振成像研究

目的研究内容记忆和来源记忆的脑区激活情况,验证单加工和双加工模型的可靠性。方法16位正常成人。实验材料为504个高频的汉字双字词。任务分四种(学习、对照、内容记忆和来源记忆任务),采用学习-任务-学习-任务设计。利用GE1.5T Signa Horizon LX成像系统采集脑部f MRI数据,通过SPM99软件对f MRI数据进行分析。结果内容记忆和来源记忆均引起双前额中回(BA6)激活。相对于来源记忆,内容记忆较多引起右前额中回(BA46)和右侧海马激活;相对于内容记忆,来源记忆较多引起左前额额中回(BA10)和左侧海马激活。另在来源记忆中,前扣带回(BA32/24),双前额叶下部(BA44/45)和小脑激活较内容记忆明显。结论内容记忆和来源记忆均引起双前额中回激活,但前者较多引起右前额中回激活,而后者较多引起左前额中回激活。内容记忆引起右侧海马激活,而来源记忆引起左侧海马激活。     

Feeling-of-knowing in episodic memory: an event-related fMRI study

An individual may fail to recall an item from memory but still feel that it would be recognized on a later test, a retrieval state termed the "feeling-of-knowing" (FOK). In this study we used event-related fMRI and the FOK to examine both encoding- and retrieval-related factors that are associated with different levels of recall performance: successful retrieval of a previously studied item, retrieval failure accompanied by the FOK, and retrieval failure without any FOK. The results revealed one predominant pattern of retrieval-related activation: an intermediate level of activation for FOK-less than that associated with successful recall and greater than that associated with unsuccessful recall (frontal and left parietal cortices). Two further patterns were also observed: greater activation for both successful recall and FOK than for unsuccessful recall (left midlateral prefrontal cortex) and greater activation for successful recall than for both FOK and unsuccessful recall (left MTL). Analysis of encoding trials conditional upon subsequent retrieval success revealed a pattern of activation that appeared to predict subsequent recall, but which further analysis indicated to be a better predictor of subsequent recognition. These results provide evidence that the phenomenology of graded recall is represented neurally in frontal and parietal cortices, but that activation at encoding may not precipitate the different levels of recall experience.     

Hemodynamic correlates of stimulus repetition in the visual and auditory cortices: an fMRI study

We examined the effects of stimulus repetition upon the evoked hemodynamic response (HDR) in auditory and visual cortices measured by magnetic resonance imaging in two experiments. Experiment 1 focused on the effects of the interval duration between two identical stimuli on HDR. Pure auditory tones (1000 Hz) of 100-ms duration were presented singly or in pairs with intrapair intervals (IPIs: onset-to-onset) of 1, 4, and 6 s. In Experiment 2, using a within-subject design, we aimed to compare the HDR refractory period in both sensory cortices as well as the HDRs to auditory and visual stimuli. Identical auditory tone as described above and visual stimuli of 500-ms high-contrast checkerboard patterns were presented singly or in identical pairs with an IPI of 1 s. Images were acquired at 1.5 T using a gradient-echo echo-planar imaging sequence sensitive to blood oxygenation level-dependent (BOLD) contrast. Experiment 1 revealed that the HDR evoked by an auditory stimulus is followed by a refractory period of 4-6 s in the auditory cortex, as indicated by smaller HDR amplitudes to the second of each pair of stimuli. Furthermore, peak latency was dependent upon IPI, with longer latencies observed for shorter IPIs. Experiment 2 revealed that the HDR evoked in both sensory cortices by paired stimulus presentations is suppressed and delayed similarly by the refractory effects imposed by the preceding stimulus, suggesting similar refractory properties of the HDR at this specific IPI. We also provide evidence for additional neural resource allocation in response to repeated stimuli.     

Superior temporal and inferior frontal cortices are activated by infrequent sound duration decrements: an fMRI study

Functional magnetic resonance imaging (fMRI) was used to examine the processing of infrequent changes occurring in an unattended sound sequence. In event-related brain potentials (ERPs), such sound changes typically elicit several responses, including an enhanced N1, the mismatch negativity (MMN), and the P3a. In the present study, subjects were presented with a repeating sound of 75 ms in duration, which was occasionally replaced, in separate blocks, by a 15-ms, 25-ms, or 35-ms sound (large, medium, and small change, respectively). In the baseline block, only the frequent 75-ms sound was presented. During the scanning, the subjects were instructed to ignore the sounds while watching a silent wildlife documentary. We assumed that in this condition, the MMN mechanism would contribute more to the observed activation than the other change-related processes. We expected sound changes to elicit fMRI activation bilaterally in the supratemporal cortices, where the electric MMN is mainly generated, and that the magnitude of this activation would increase with the magnitude of sound duration change. Unexpectedly, however, we found that only blocks with medium duration changes (25 ms) showed significant activation in the supratemporal cortex. In addition, as reported in some previous EEG and fMRI studies, contrasts between different levels of sound duration change revealed additional activation in the inferior frontal cortex bilaterally. This activation tended to be greater for the small and medium changes than for the large ones.     

The human prefrontal and parietal association cortices are involved in NO-GO performances: an event-related fMRI study

One of the important roles of the prefrontal cortex is inhibition of movement. We applied an event-related functional magnetic resonance imaging (fMRI) technique to observe changes in fMRI signals of the entire brain during a GO/NO-GO task to identify the functional fields activated in relation to the NO-GO decision. Eleven normal subjects participated in the study, which consisted of a random series of 30 GO and 30 NO-GO trials. The subjects were instructed to press a mouse button immediately after the GO signal was presented. However, they were instructed not to move when the NO-GO signal was presented. We detected significant changes in MR signals in relation to the preparation phases, GO responses, and NO-GO responses. The activation fields related to the NO-GO responses were located in the bilateral middle frontal cortices, left dorsal premotor area, left posterior intraparietal cortices, and right occipitotemporal area. The fields of activation in relation to the GO responses were found in the left primary sensorimotor, right cerebellar anterior lobule, bilateral thalamus, and the area from the anterior cingulate to the supplementary motor area (SMA). Brain activations related to the preparation phases were identified in the left dorsal premotor, left lateral occipital, right ventral premotor, right fusiform, and the area from the anterior cingulate to the SMA. The results indicate that brain networks consisting of the bilateral prefrontal, intraparietal, and occipitotemporal cortices may play an important role in executing a NO-GO response.     

Neural substrates of cross-modal olfactory recognition memory: an fMRI study

Ten young adults (aged 20 to 25 years) participated in a functional Magnetic Resonance Imaging (fMRI) study to investigate neural substrates of cross-modal olfactory recognition memory. Before entering the scanner, participants were presented with 16 familiar odors selected from the COLT (Murphy, C., Nordin, S., Acosta, L., 1997. Odor learning, recall, and recognition memory in young and elderly adults. Neuropsychology 11, 126-137) and were then scanned for 3 runs according to a paradigm derived from Stark and Squire (Stark, C.E., Squire, L.R., 2000. Functional magnetic resonance imaging (fMRI) activity in the hippocampal region during recognition memory. J. Neurosci. 20, 7776-7781). During each run, participants were shown names of odors presented (targets) or not presented (foils) at encoding. Participants distinguished targets from foils via button press. Each run alternated 4 'ON' periods containing 7 targets and 2 foils (36 s) and 4 'OFF' periods with 7 foils and 2 targets (36 s). Data were processed with AFNI (Cox, R.W., 1996. AFNI: software for analysis and visualization of functional magnetic resonance neuroimages. Comput. Biomed. Res. 29, 162-173) and compared ON and OFF periods, extracting activation in regions that responded during the cross-modal olfactory recognition memory task. Group analysis showed that regions activated during the first run included right hippocampus, piriform/amygdalar area, superior temporal gyrus, anterior cingulate gyrus, inferior frontal/orbitofrontal gyrus, superior/medial frontal gyrus, and bilateral parahippocampal gyrus, inferior parietal lobule, supramarginal gyrus, cerebellum, lingual/fusiform area and middle/posterior cingulate gyrus. Region of interest analysis showed that degree of activation significantly decreased from run 1 to run 3 in the right hippocampus, fusiform gyrus, lingual gyrus, parahippocampal gyrus and middle frontal gyrus but not in other regions, suggesting that these regions sustain a specific function in olfactory recognition memory that attenuates as foils become more familiar with repeated presentation.     

Visual feature and conjunction searches of equal difficulty engage only partially overlapping frontoparietal networks.

According to a classical view of visual object recognition, targets are detected "pre-attentively" if they carry unique features, whereas attention has to be deployed serially to object locations for feature binding if the targets can be distinguished from distracters only in terms of their feature conjunctions. Consistent with this view, recent reports suggest a contribution of the posterior parietal cortex (PPC; one major region controlling spatial attention) to conjunction search as opposed to feature search. However, PPC engagement in conjunction search might also reflect feature-based attention or the difficulty of target selection. The present fMRI study compared regions and amplitudes of cortical activity reflecting the attention mechanisms of a conjunction and a feature search of equal difficulty performed during maintenance of fixation. Attention-related activity was assessed by comparing each hard feature and conjunction search with an easy feature search. Hard feature and conjunction search activated overlapping regions in multiple PPC areas and in the frontal eye field (FEF). Most consistent PPC overlaps were located in the anterior and posterior intraparietal sulcus (IPS). The response amplitude of posterior IPS did not differ between both search tasks. However, the IPS junction with the transverse occipital sulcus and the FEF responded at a higher amplitude during conjunction search. Moreover, regions of the prefrontal cortex and the PPC were activated only during either hard feature or conjunction search. These findings suggest that equally difficult visual searches for features and conjunctions are controlled by overlapping frontoparietal networks, but also that both search types involve specific mechanisms.     

Maintenance versus manipulation in verbal working memory revisited: an fMRI study

Working memory (WM) is the ability to keep a limited amount of information "on line" for immediate use during short intervals. Verbal WM has been hypothesized to consist of neuroanatomically segregated components, i.e., maintenance (storage, rehearsal, and matching) and manipulation (reordering or updating), corresponding to ventrolateral and dorsolateral prefrontal cortex. Previous imaging studies of maintenance vs manipulation processes in WM have produced inconsistent results, which may have been due to methodological issues such as low statistical power and the use of insertion (subtraction) designs. In the present functional magnetic resonance imaging study we used parametric versions of both a prototypical maintenance task (Sternberg) and a prototypical manipulation task (n-letter back task) in 21 healthy subjects. Increased signal correlated with load common for both tasks was found in bilateral dorsolateral and anterior prefrontal, left ventrolateral prefrontal, and bilateral parietal regions. Workload x task interactions were found in bilateral dorsolateral prefrontal cortex for manipulation vs maintenance, but also for responding vs encoding (storage) in the maintenance task. Therefore, our data support a functional rather than a neuroanatomical distinction between maintenance and manipulation, given our finding that these tasks differentially activate virtually identical systems.     

View-independent coding of face identity in frontal and temporal cortices is modulated by familiarity: an event-related fMRI study

Face recognition is a unique visual skill enabling us to recognize a large number of person identities, despite many differences in the visual image from one exposure to another due to changes in viewpoint, illumination, or simply passage of time. Previous familiarity with a face may facilitate recognition when visual changes are important. Using event-related fMRI in 13 healthy observers, we studied the brain systems involved in extracting face identity independent of modifications in visual appearance during a repetition priming paradigm in which two different photographs of the same face (either famous or unfamiliar) were repeated at varying delays. We found that functionally defined face-selective areas in the lateral fusiform cortex showed no repetition effects for faces across changes in image views, irrespective of pre-existing familiarity, suggesting that face representations formed in this region do not generalize across different visual images, even for well-known faces. Repetition of different but easily recognizable views of an unfamiliar face produced selective repetition decreases in a medial portion of the right fusiform gyrus, whereas distinct views of a famous face produced repetition decreases in left middle temporal and left inferior frontal cortex selectively, but no decreases in fusiform cortex. These findings reveal that different views of the same familiar face may not be integrated within a single representation at initial perceptual stages subserved by the fusiform face areas, but rather involve later processing stages where more abstract identity information is accessed.     

Ecphory of autobiographical memories: an fMRI study of recent and remote memory retrieval

Ecphory occurs when one recollects a past event cued by a trigger, such as a picture, odor, or name. It is a central component of autobiographical memory, which allows us to "travel mentally back in time" and re-experience specific events from our personal past. Using fMRI and focusing on the role of medial temporal lobe (MTL) structures, we investigated the brain bases of autobiographical memory and whether they change with the age of memories. Importantly, we used an ecphory task in which the remote character of the memories was ensured. The results showed that a large bilateral network supports autobiographical memory: temporal lobe, temporo-parieto-occipital junction, dorsal prefrontal cortex, medial frontal cortex, retrosplenial cortex and surrounding areas, and MTL structures. This network, including MTL structures, changed little with the age of the memories.     

Increased frontocerebellar activation in alcoholics during verbal working memory: an fMRI study

Although there is clear evidence of alcoholism-related damage to the frontal lobes and cerebellum from neuroimaging, neuropathological, and neuropsychological studies, the functional role of the cerebellum and cerebrocerebellar circuits related to verbal working memory deficits of alcoholics have not been well studied. Alcoholic and nonalcoholic subjects performed a Sternberg verbal working memory task while receiving an fMRI scan in a 3T magnet. This task has been found in previous studies to reliably activate the articulatory control and phonological storage components of the phonological loop (left frontal, left temporal/parietal structures, right superior cerebellar regions) in young healthy controls. We hypothesized that the alcoholics would show a different pattern of activation from the controls, based on the regions of interest (ROIs) identified from a previous study of healthy subjects. Behavioral results showed the alcoholics to be performing at a comparable level to the matched controls in terms of accuracy and median reaction time, with no statistically significant differences. However, analysis of the functional data revealed that the alcoholics exhibited greater activation in the left frontal (BA44/45) and right superior cerebellum (HVI) regions relative to the matched controls. These findings suggest that brain activation in left frontal and right cerebellar regions that support the articulatory control system of verbal working memory may require a compensatory increase in alcoholics in order to maintain the same level of performance as controls.     

The effect of adult-acquired hippocampal damage on memory retrieval: an fMRI study

Bilateral hippocampal pathology typically results in significant memory problems. Despite apparently similar structural damage, patients with such lesions can differ in the pattern of impairment and preservation of memory functions. Previously, an fMRI study of a developmental amnesic patient whose anoxic hippocampal damage was incurred perinatally revealed his residual hippocampal tissue to be active during memory retrieval. This hippocampal activity was apparent during the retrieval of personal and general facts relative to a control task. In this study, we used a similar fMRI paradigm to investigate whether residual hippocampal activation was present also in patient VC with adult-acquired anoxic hippocampal pathology. VC's performance and reaction times on the experimental personal and general fact tasks were comparable to age-matched control subjects. However, in contrast to the elderly control sample and the previous developmental amnesic patient, his residual hippocampal tissue did not show activation changes during the experimental tasks. This finding indicates that patient VC's successful retrieval of personal and general facts was achieved without a significant hippocampal contribution. It further suggests that the hippocampal activation observed in the elderly controls and previous developmental amnesic patient was not necessary for successful task performance. The reason for this difference in hippocampal responsivity between VC and the developmental amnesic patient remains to be determined. We speculate that it may relate to the age at which hippocampal damage occurred reflecting plasticity within the developing brain, or to cognitive differences between VC, the developmental amnesic patient, and the control subjects.     

Age-related changes in working memory during sentence comprehension: an fMRI study.

Sentence comprehension declines with age, but the neural basis for this change is unclear. We monitored regional brain activity in 13 younger subjects and 11 healthy seniors matched for sentence comprehension accuracy while they answered a simple probe about written sentences. The sentences varied in their grammatical features (subject-relative vs object-relative subordinate clause) and their verbal working memory (WM) demands (short vs long antecedent noun-gap linkage). We found that young and senior subjects both recruit a core written sentence processing network, including left posterolateral temporal and bilateral occipital cortex for all sentences, and ventral portions of left inferior frontal cortex for object-relative sentences with a long noun-gap linkage. Differences in activation patterns for seniors compared to younger subjects were due largely to changes in brain regions associated with a verbal WM network. While seniors had less left parietal recruitment than younger subjects, left premotor cortex, and dorsal portions of left inferior frontal cortex showed greater activation in seniors compared to younger subjects. Younger subjects recruited right posterolateral temporal cortex for sentences with a long noun-gap linkage. Seniors additionally recruited right parietal cortex for this sentence-specific form of WM. Our findings are consistent with the hypothesis that the neural basis for sentence comprehension includes dissociable but interactive large-scale neural networks supporting core written sentence processes and related cognitive resources involved in WM. Seniors with good comprehension appear to up-regulate portions of the neural substrate for WM during sentence processing to achieve comprehension accuracy that equals young subjects.     

The role of the prefrontal cortex in recognition memory and memory for source: an fMRI study.

We employed fMRI to index neural activity in prefrontal cortex during tests of recognition and source memory. At study, subjects were presented with words displayed either to the left or right of fixation, and, depending on the side, performed one of two orienting tasks. The test phase consisted of a sequence of three 10-word blocks, displayed in central vision. For one block, subjects performed recognition judgements on a mixture of two old and eight new words (low density recognition). For another block, recognition judgements were performed on a mixture of eight old and two new words (high density recognition). In the remaining block, also consisting of eight old and two new items, the requirement was to judge whether each word had been presented at study on the left or the right. Relative to the low density condition, high density recognition was associated with increased activity in right and, to a lesser extent, left, anterior prefrontal cortex (BA 10), replicating the findings of two previous PET studies. Right anterior prefrontal activity did not show any further increase during the source task. Instead, greater activity was found, relative to high density recognition, in left BA 10, left inferior frontal gyrus (BA 45/47), and bilateral opercular cortices (BA 45/47). The findings are inconsistent with the proposal that activation of right anterior prefrontal cortex during memory retrieval reflects "postretrieval" processing demands, such demands being considerably greater for judgments of source than recognition. The findings provide further evidence that the left prefrontal cortex plays a role in episodic memory retrieval when the task explicitly requires recovery of contextual as well as item information.     

Multilingualism: an fMRI study

To investigate the hypothesis that in multilingual speakers different languages are represented in distinct brain regions, 12 multilingual right-handed men performed a word fluency task, a picture naming task, a comprehension reading task, and their respective control tasks in three languages (Dutch, French, and English) while whole-head functional magnetic resonance imaging (fMRI) was applied. In general, all language tasks revealed predominantly overlapping regions of activation for the different languages. Cerebral activation during use of the foreign languages showed a tendency toward a more extensive recruitment of the areas activated in the native language and the activation of a greater number of regions. Word generation in the foreign languages elicited additional bilateral inferior frontal activation, including Broca's area and left middle temporal gyrus activation; in the native language, additional postcentral activation was found. Picture naming in the foreign languages recruited additional inferior-lateral and medial frontal regions predominantly on the left, and more posterior right hemispheric activation in the mother tongue. During comprehension reading there was more activation in medial posterior regions in the native language. Our results suggest that the performance of language tasks in different languages engages largely the same cerebral areas but that the brain, to perform at a comparable proficiency level, engages more neural substrates for later acquired languages. Our findings do not support the view that languages learned later in life entail more right hemispheric involvement. Finally, a consequent effect of language exposure was found for reading, where increased familiarity engages more occipital activation whereas decreased familiarity appears to be associated with increased left hemispheric inferior frontal activation.     

Visual imagery of famous faces: effects of memory and attention revealed by fMRI

Complex pictorial information can be represented and retrieved from memory as mental visual images. Functional brain imaging studies have shown that visual perception and visual imagery share common neural substrates. The type of memory (short- or long-term) that mediates the generation of mental images, however, has not been addressed previously. The purpose of this study was to investigate the neural correlates underlying imagery generated from short- and long-term memory (STM and LTM). We used famous faces to localize the visual response during perception and to compare the responses during visual imagery generated from STM (subjects memorized specific pictures of celebrities before the imagery task) and imagery from LTM (subjects imagined famous faces without seeing specific pictures during the experimental session). We found that visual perception of famous faces activated the inferior occipital gyri, lateral fusiform gyri, the superior temporal sulcus, and the amygdala. Small subsets of these face-selective regions were activated during imagery. Additionally, visual imagery of famous faces activated a network of regions composed of bilateral calcarine, hippocampus, precuneus, intraparietal sulcus (IPS), and the inferior frontal gyrus (IFG). In all these regions, imagery generated from STM evoked more activation than imagery from LTM. Regardless of memory type, focusing attention on features of the imagined faces (e.g., eyes, lips, or nose) resulted in increased activation in the right IPS and right IFG. Our results suggest differential effects of memory and attention during the generation and maintenance of mental images of faces.     

Somatotopic organization of human somatosensory cortices for pain: a single trial fMRI study

The ability to locate pain plays a pivotal role in immediate defense and withdrawal behavior. However, how the brain localizes nociceptive information without additional information from somatotopically organized mechano-receptive pathways is not well understood. To investigate the somatotopic organization of the nociceptive system, we applied Thulium-YAG-laser evoked pain stimuli, which have no concomitant tactile component, to the dorsum of the left hand and foot in randomized order. We used single-trial functional magnetic resonance imaging (fMRI) to assess differential hemodynamic responses to hand and foot stimulation for the group and in a single subject approach. The primary somatosensory cortex (SI) shows a clear somatotopic organization ipsi- and contralaterally to painful stimulation. Furthermore, a differential representation of hand and foot stimulation appeared within the contralateral opercular--insular region of the secondary somatosensory cortex (SII). This result provides evidence that both SI and SII encode spatial information of nociceptive stimuli without additional information from the tactile system and highlights the concept of a redundant representation of basic discriminative stimulus features in human somatosensory cortices, which seems adequate in view of the evolutionary importance of pain perception.     

Frontal activations associated with accessing and evaluating information in working memory: an fMRI study

To investigate the involvement of frontal cortex in accessing and evaluating information in working memory, we used a variant of a Sternberg paradigm and compared brain activations between positive and negative responses (known to differentially tax access/evaluation processes). Participants remembered two trigrams in each trial and were then cued to discard one of them and maintain the other one as the target set. After a delay, a probe letter was presented and participants made decisions about whether or not it was in the target set. Several frontal areas--anterior cingulate (BA32), middle frontal gyrus (bilateral BA9, right BA10, and right BA46), and left inferior frontal gyrus (BA44/45)--showed increased activity when participants made correct negative responses relative to when they made correct positive responses. No areas activated significantly more for the positive responses than for the negative responses. It is suggested that the multiple frontal areas involved in the test phase of this task may reflect several component processes that underlie more general frontal functions.     

Load- and practice-dependent increases in cerebro-cerebellar activation in verbal working memory: an fMRI study

Load-dependent and practice-related changes in neocortical and cerebellar structures involved in verbal working memory (VWM) were investigated using functional MRI (fMRI) and a two alternative forced choice Sternberg paradigm. Using working memory loads ranging from 2 to 6 letters, regions exhibiting linear and quadratic trends in load-dependent activations were identified. Behaviorally, reaction time measurements revealed significant linear increases with increasing memory load, and significant decreases with increased task practice. Brain activations indicated a preponderance of linear load-dependent responses in both superior (lobule VI/Crus I) and inferior (lobule VIIB/VIIIA) cerebellar hemispheres, as well as in areas of neocortex including left precentral (BA 6), inferior frontal (BA 47), parahippocampal (BA 35), inferior parietal (BA 40), cingulate (BA 32), and right inferior and middle frontal (BA 46/47) regions. Fewer voxels exhibited quadratic without linear trends with the most prominent of these activations located in left inferior parietal (BA 40), precuneus, and parahippocampal regions. Analysis of load x session interactions revealed that right inferior cerebellar and left inferior parietal activations increased with practice, as did the correlations between activation in each region with reaction time, suggesting that changes in this cerebro-cerebellar network underlie practice-related increases in efficiency of VWM performance. These results replicate and extend our previous findings of fMRI activation in the cerebellum during VWM, and demonstrate predominately linear increases in cerebro-cerebellar activation with increasing memory load as well as changes in network function with increased task proficiency.