Object activation from features in the semantic system

A modified neural circuit framework for semantic memory retrieval with implications for circuit modulation to treat verbal retrieval deficits

Word finding difficulty is a frequent complaint in older age and disease states, but treatment options are lacking for such verbal retrieval deficits. Better understanding of the neurophysiological and neuroanatomical basis of verbal retrieval function may inform effective interventions. In this article, we review the current evidence of a neural retrieval circuit central to verbal production, including words and semantic memory, that involves the pre-supplementary motor area (pre-SMA), striatum (particularly caudate nucleus), and thalamus. We aim to offer a modified neural circuit framework expanded upon a memory retrieval model proposed in 2013 by Hart et al., as evidence from electrophysiological, functional brain imaging, and noninvasive electrical brain stimulation studies have provided additional pieces of information that converge on a shared neural circuit for retrieval of memory and words. We propose that both the left inferior frontal gyrus and fronto-polar regions should be included in the expanded circuit. All these regions have their respective functional roles during verbal retrieval, such as selection and inhibition during search, initiation and termination of search, maintenance of co-activation across cortical regions, as well as final activation of the retrieved information. We will also highlight the structural connectivity from and to the pre-SMA (e.g., frontal aslant tract and fronto-striatal tract) that facilitates communication between the regions within this circuit. Finally, we will discuss how this circuit and its correlated activity may be affected by disease states and how this circuit may serve as a novel target engagement for neuromodulatory treatment of verbal retrieval deficits.

Differences in electroencephalography oscillations between normal aging and mild cognitive impairment during semantic memory retrieval

Semantic memory remains relatively stable with normal cognitive aging and declines in early stages of neurodegenerative disease. We measured electroencephalography (EEG) oscillatory correlates of semantic memory retrieval to examine the effects of normal and pathological aging. Twenty-nine cognitively healthy young adults (YA), 22 cognitively healthy aging adults (HA) and 20 patients with mild cognitive impairment (MCI) completed a semantic memory retrieval task with concurrent EEG recording in which they judged whether two words (features of objects) led to retrieval of an object (retrieval) or not (non-retrieval). Event-related power changes contrasting the two conditions (retrieval vs. non-retrieval) within theta, alpha, low-beta and high-beta EEG frequency bands were examined for normal aging (YA vs. HA) and pathological aging effects (HA vs. MCI). With no behavioural differences between the two normal age groups, we found later theta and alpha event-related power differences between conditions only in YA and a high-beta event-related power difference only in HA. For pathological aging effects, with reduced accuracy in MCI, we found different EEG patterns of early event-related beta power differences between conditions in MCI compared with HA and an event-related low-beta power difference only in HA. Beta oscillations were correlated with behavioural performance only in HA. We conclude that the aging brain relies on faster (beta) oscillations during the semantic memory task. With pathological aging, retrieval accuracy declines and pattern of beta oscillation changes. The findings provide insights about age-related neural mechanisms underlying semantic memory and have implications for early detection of pathological aging.

Two different brain networks underlying picture naming with familiar pre-existing native words and new vocabulary

The present research used fMRI to longitudinally investigate the impact of learning new vocabulary on the activation pattern of the language control network by measuring BOLD signal changes during picture naming tasks with familiar pre-existing native words (old words) and new vocabulary. Nineteen healthy participants successfully learned new synonyms for already known Spanish words, and they performed a picture naming task using the old words and the new words immediately after learning and two weeks after learning. The results showed that naming with old words, compared to naming with newly learned words, produced activations in a cortical network involving frontal and parietal regions, whereas the opposite contrast showed activation in a broader cortical/subcortical network, including the SMA/ACC, the hippocampus, and the midbrain. These two networks are maintained two weeks after learning. These results suggest that the language control network can be separated into two functional circuits for diverse cognitive purposes.

Thalamic Aphasia: a Review

PURPOSE OF REVIEW

Thalamic aphasia is a rare language disorder resulting from lesions to the thalamus. While most patients exhibit mild symptoms with a predominance of lexical-semantic difficulties, variations in phenotype have been described. Overall, the exact mechanisms of thalamic aphasia await empirical research. The article reviews recent findings regarding phenotypes and possible underlying mechanisms of thalamic aphasia.

RECENT FINDINGS

Variations in phenotype of thalamic aphasia may be related to different lesion locations. Overall, the thalamus' role in language is thought to be due to its involvement in cortico-thalamic language networks with lesioning of certain nuclei resulting in the diachisis of otherwise interconnected areas. Its possible monitoring function in such a network might be due to its different cellular firing modes. However, no specific evidence has been collected to date. While recent findings show a more distinct understanding of thalamic aphasia phenotypes and possible underlying mechanisms, further research is needed. Additionally, as standard language testing might oftentimes not pick up on its subtle symptoms, thalamic aphasia might be underdiagnosed.

The Role of the Thalamus in Declarative and Procedural Linguistic Memory Processes

Typically, thalamic aphasias appear to be primarily lexical-semantic disorders representing difficulty using stored declarative memories for semantic information to access lexical word forms. Yet, there also is reason to believe that the thalamus might play a role in linguistic procedural memory. For more than two decades, we have known that basal ganglia dysfunction is associated with difficulties in procedural learning, and specific thalamic nuclei are the final waypoint back to the cortex in cortico-basal ganglia-cortical loops. Recent analyses of the role of the thalamus in lexical-semantic processes and of the role of the basal ganglia in linguistic processes suggest that thalamic participation is not simply a matter of declarative vs. procedural memory, but a matter of how the thalamus participates in lexical-semantic processes and in linguistic procedural memory, as well as the interaction of these processes. One role for the thalamus in accessing lexical forms for semantic concepts relates to the stabilization of a very complex semantic-lexical interface with thousands of representations on both sides of the interface. Further, the possibility is discussed that the thalamus, through its participation in basal ganglia loops, participates in two linguistic procedural memory processes: syntactic/grammatical procedures and procedures for finding words to represent semantic concepts, with the latter interacting intricately with declarative memories. These concepts are discussed in detail along with complexities that can be addressed by future research.

Identification of selection and inhibition components in a Go/NoGo task from EEG spectra using a machine learning classifier

INTRODUCTION

Prior Go/NoGo studies have localized specific regions and EEG spectra for which traditional approaches have distinguished between Go and NoGo conditions. A more detailed characterization of the spatial distribution and timing of the synchronization of frequency bands would contribute substantially to the clarification of neural mechanisms that underlie performance of the Go/NoGo task.

METHODS

The present study used a machine learning approach to learn the features that distinguish between ERSPs involved in selection and inhibition in a Go/NoGo task. A single-layer neural network classifier was used to predict task conditions for each subject to characterize ERSPs associated with Go versus NoGo trials.

RESULTS

The final classifier accurately identified individual task conditions at an overall rate of 92%, estimated by fivefold cross-validation. The detailed accounting of EEG time-frequency patterns localized to brain regions (i.e., thalamus, pre-SMA, orbitofrontal cortex, and superior parietal cortex) corroborates and also elaborates upon previous findings from fMRI and EEG studies, and expands the information about EEG power changes in multiple frequency bands (i.e., primarily theta power increase, alpha decreases, and beta increases and decreases) within these regions underlying the selection and inhibition processes engaged in the Go and NoGo trials.

CONCLUSION

This time-frequency-based classifier extends previous spatiotemporal findings and provides information about neural mechanisms underlying selection and inhibition processes engaged in Go and NoGo trials, respectively. This neural network classifier can be used to assess time-frequency patterns from an individual subject and thus may offer insight into therapeutic uses of neuromodulation in neural dysfunction.

Local and whole-network topologies reveal that pulvinar and semantic hub interactions correlate with picture vocabulary

Evidence from cognitive neuroscience indicates that subcortical regions, especially the pulvinar region of the thalamus, are involved in semantic processing. In the current study, graph-based methods were used to investigate whether a cortical-subcortical network is involved in vocabulary processing. In addition to traditional resting-state functional connectivity (rsFC) analysis between local brain areas, we applied a novel method to validate the interaction between semantic network hubs and the pulvinar. Unlike the traditional rsFC, the new metrics assessed rsFC pattern similarity (rsFCS), which was calculated with a cosine similarity algorithm based on whole-network topological information. We also applied a support vector regression program based on left pulvinar connectivity patterns. A brain-behavior analysis was conducted based on 100 randomly selected unrelated participants from the Human Connectome Project S1200 database. After controlling for the visuospatial and attention test scores, the rsFC between the left middle temporal gyrus, left inferior parietal lobule, and left pulvinar was significantly positively correlated with age-adjusted picture vocabulary scores. Similar results were confirmed based on the new rsFCS analysis. The support vector regression procedures also showed a clearly relationship between picture vocabulary scores and left pulvinar-related rsFCs. Our study verified a role for a subcortical-cortical network in vocabulary processing that is based on local and whole-network topologies.

Multimodal feature binding in object memory retrieval using event-related potentials: Implications for models of semantic memory

To test the hypothesis that semantic processes are represented in multiple subsystems, we recorded electroencephalogram (EEG) as we elicited object memories using the modified Semantic Object Retrieval Test, during which an object feature, presented as a visual word [VW], an auditory word [AW], or a picture [Pic], was followed by a second feature always presented as a visual word. We performed both hypothesis-driven and data-driven analyses using event-related potentials (ERPs) time locked to the second stimulus. We replicated a previously reported left fronto-temporal ERP effect (750-1000 ms post-stimulus) in the VW task, and also found that this ERP component was only present during object memory retrieval in verbal (VW, AW) as opposed to non-verbal (Pic) stimulus types. We also found a right temporal ERP effect (850-1000 ms post-stimulus) that was present in auditory (AW) but not in visual (VW, Pic) stimulus types. In addition, we found an earlier left temporo-parietal ERP effect between 350 and 700 ms post-stimulus and a later midline parietal ERP effect between 700 and 1100 ms post-stimulus, present in all stimulus types, suggesting common neural mechanisms for object retrieval processes and object activation, respectively. These findings support multiple semantic subsystems that respond to varying stimulus modalities, and argue against an ultimate unitary amodal semantic analysis.

The Role of Cortico-Thalamo-Cortical Circuits in Language: Recurrent Circuits Revisited

Based on a review of recent literature, a recurrent circuit model describes how cortico-thalamo-cortical and cortico-cortical circuitry supports word retrieval, auditory-verbal comprehension, and other language functions. Supporting data include cellular and layer-specific cortico-thalamic, thalamo-cortical, and cortico-cortical neuroanatomy and electrophysiology. The model posits that during word retrieval, higher order cortico-thalamo-cortical relays maintain stable representations of semantic information in feedforward processes at the semantic-lexical interface. These stable semantic representations are compared to emerging lexical solutions to represent the semantic construct to determine how well constructs are associated with each other. The resultant error signal allows cortico-cortical sculpting of activity between the semantic and lexical mechanisms until there is a good match between these two levels, at which time the lexical solution will be passed along to the cortical processor necessary for the next stage of word retrieval. Evidence is cited that high gamma activity is the neural signature for processing in the cortico-thalamo-cortical and cortico-cortical circuitry. Methods for testing hypotheses generated from this recurrent circuit model are discussed. Mathematical modeling may be a useful tool in exploring underlying properties of these circuits.

High-Definition Transcranial Direct Current Stimulation to Improve Verbal Retrieval Deficits in Chronic Traumatic Brain Injury

Chronic verbal retrieval deficits have been noted in traumatic brain injury (TBI), but no U.S. Food and Drug Administration-approved interventions are available. The present study investigated whether 10 sessions of 20 min of 1 mA anodal high-definition transcranial direct current stimulation (HD-tDCS) targeting pre-supplementary motor area/dorsal anterior cingulate cortex (preSMA/dACC) compared with sham HD-tDCS would improve verbal retrieval deficits in TBI patients. Improvements in verbal retrieval processes were observed up to 8 weeks post-treatment. Thus, potential dysfunction to verbal retrieval circuitry in TBI appears amenable to remediation through electromodulation with HD tDCS to the preSMA/dACC. Although further studies clarifying mechanisms by which tDCS brought about these improvements will likely inform refinements in the application of this therapeutic technique, the findings suggest the efficacy of using HD-tDCS to target other systems vulnerable to TBI to improve functioning.

Thalamic deep brain stimulation decelerates automatic lexical activation

BACKGROUND

Deep Brain Stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) is a therapeutic option for patients with essential tremor. Despite a generally low risk of side effects, declines in verbal fluency (VF) have previously been reported.

OBJECTIVES

We aimed to specify effects of VIM-DBS on major cognitive operations needed for VF task performance, represented by clusters and switches. Clusters are word production spurts, thought to arise from automatic activation of associated information pertaining to a given lexical field. Switches are slow word-to-word transitions, presumed to indicate controlled operations for stepping from one lexical field to another.

PATIENTS & METHODS

Thirteen essential tremor patients with VIM-DBS performed verbal fluency tasks in their VIM-DBS ON and OFF conditions. Clusters and switches were formally defined by mathematical criteria. All results were compared to those of fifteen healthy control subjects, and significant OFF-ON-change scores were correlated to stimulation parameters.

RESULTS

Patients produced fewer words than healthy controls. DBS ON compared to DBS OFF aggravated this deficit by prolonging the intervals between words within clusters, whereas switches remained unaffected. This stimulation effect correlated with more anterior electrode positions.

CONCLUSION

VIM-DBS seems to influence word output dynamics during verbal fluency tasks on the level of word clustering. This suggests a perturbation of automatic lexical co-activation by thalamic stimulation, particularly if delivered relatively anteriorly. The findings are discussed in the context of the hypothesized role of the thalamus in lexical processing.

Electrophysiological Correlates of Word Retrieval in Traumatic Brain Injury

Persons who have had a traumatic brain injury (TBI) often have word retrieval deficits; however, the underlying neural mechanisms of such deficits are yet to be clarified. Previous studies in normal subjects have shown that during a word retrieval task, there is a 750 msec event-related potential (ERP) divergence detected at the left fronto-temporal region when subjects evaluate word pairs that facilitate retrieval compared with responses elicited by word pairs that do not facilitate retrieval. In this study, we investigated the neurophysiological correlates of word retrieval networks in 19 retired professional athletes with TBI and 19 healthy control (HC) subjects. We recorded electroencephalography (EEG) in the participants during a semantic object retrieval task. In this task, participants indicated whether presented word pairs did (retrieval) or did not (non-retrieval) facilitate the retrieval of an object name. There were no significant differences in accuracy or reaction time between the two groups. The EEG showed a significant group by condition interaction over the left fronto-temporal region. The HC group mean amplitudes were significantly different between conditions, but the TBI group data did not show this difference, suggesting neurophysiological effects of injury. These findings provide evidence that ERP amplitudes may be used as a marker of disrupted semantic retrieval circuits in persons with TBI even when those persons perform normally.

Altered Neural Activity during Semantic Object Memory Retrieval in Amnestic Mild Cognitive Impairment as Measured by Event-Related Potentials

Deficits in semantic memory in individuals with amnestic mild cognitive impairment (aMCI) have been previously reported, but the underlying neurobiological mechanisms remain to be clarified. We examined event-related potentials (ERPs) associated with semantic memory retrieval in 16 individuals with aMCI as compared to 17 normal controls using the Semantic Object Retrieval Task (EEG SORT). In this task, subjects judged whether pairs of words (object features) elicited retrieval of an object (retrieval trials) or not (non-retrieval trials). Behavioral findings revealed that aMCI subjects had lower accuracy scores and marginally longer reaction time compared to controls. We used a multivariate analytical technique (STAT-PCA) to investigate similarities and differences in ERPs between aMCI and control groups. STAT-PCA revealed a left fronto-temporal component starting at around 750 ms post-stimulus in both groups. However, unlike controls, aMCI subjects showed an increase in the frontal-parietal scalp potential that distinguished retrieval from non-retrieval trials between 950 and 1050 ms post-stimulus negatively correlated with the performance on the logical memory subtest of the Wechsler Memory Scale-III. Thus, individuals with aMCI were not only impaired in their behavioral performance on SORT relative to controls, but also displayed alteration in the corresponding ERPs. The altered neural activity in aMCI compared to controls suggests a more sustained and effortful search during object memory retrieval, which may be a potential marker indicating disease processes at the pre-dementia stage.

Effects of thalamic deep brain stimulation on spontaneous language production

The thalamus is thought to contribute to language-related processing, but specifications of this notion remain vague. An assessment of potential effects of thalamic deep brain stimulation (DBS) on spontaneous language may help to delineate respective functions. For this purpose, we analyzed spontaneous language samples from thirteen (six female / seven male) patients with essential tremor treated with DBS of the thalamic ventral intermediate nucleus (VIM) in their respective ON vs. OFF conditions. Samples were obtained from semi-structured interviews and examined on multidimensional linguistic levels. In the VIM-DBS ON condition, participants used a significantly higher proportion of paratactic as opposed to hypotactic sentence structures. This increase correlated negatively with the change in the more global cognitive score, which in itself did not change significantly. In conclusion, VIM-DBS appears to induce the use of a simplified syntactic structure. The findings are discussed in relation to concepts of thalamic roles in language-related cognitive behavior.

Imaging Correlates of Memory and Concussion History in Retired National Football League Athletes

IMPORTANCE

To our knowledge, this is the first study to show an association between concussion, cognition, and anatomical structural brain changes across the age spectrum in former National Football League athletes.

OBJECTIVE

To assess the relationship of hippocampal volume, memory performance, and the influence of concussion history in retired National Football League athletes with and without mild cognitive impairment (MCI).

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study assessed differences between groups, mean hippocampal volumes, and memory performance by computing age quintiles based on group-specific linear regression models corrected for multiple comparisons for both athletes and control participants. The study was conducted starting in November 2010 and is ongoing at a research center in the northern region of Texas. This current analysis was conducted from October 9, 2013, to August 21, 2014. Participants included 28 retired National Football League athletes, 8 of whom had MCI and a history of concussion, 21 cognitively healthy control participants, and 6 control participants with MCI without concussion.

MAIN OUTCOMES AND MEASURES

Hippocampal volume, age, California Verbal Learning Test scores, and the number of grade 3 (G3) concussions. In addition, the number of games played was examined as an objective variable pertaining to football history.

RESULTS

The mean (SD) age was 58.1 (13) years for the 28 former athletes and 59.0 (12) years for the 27 control participants. Retired athletes with concussion history but without cognitive impairment had normal but significantly lower California Verbal Learning Test scores compared with control participants (mean [SD], 52.5 [8] vs 60.24 [7]; P = .002); those with a concussion history and MCI performed worse (mean [SD], 37 [8.62]) compared with both control participants (P < .001) and athletes without memory impairment (P < .001). Among the athletes, 17 had a G3 concussion and 11 did not. Older retired athletes with at least 1 G3 concussion had significantly smaller bilateral hippocampal volumes compared with control participants at the 40th age percentile (left, P = .04; right, P = .03), 60th percentile (left, P = .009; right, P = .01), and 80th percentile (left, P = .001; right, P = .002) and a smaller right hippocampal volume compared with athletes without a G3 concussion at the 40th percentile (P = .03), 60th percentile (P = .02), and 80th percentile (P = .02). Athletes with a history of G3 concussion were more likely to have MCI (7 of 7) compared with retired athletes without a history of G3 concussion (1 of 5) older than 63 years (P = .01). In addition, the left hippocampal volume in retired athletes with MCI and concussion was significantly smaller compared with control participants with MCI (P = .03).

CONCLUSION AND RELEVANCE

Prior concussion that results in loss of consciousness is a risk factor for increased hippocampal atrophy and the development of MCI. In individuals with MCI, hippocampal volume loss appears greater among those with a history of concussion.

Broca's area - thalamic connectivity

Broca's area is crucially involved in language processing. The sub-regions of Broca's area (pars triangularis, pars opercularis) presumably are connected via corticocortical pathways. However, growing evidence suggests that the thalamus may also be involved in language and share some of the linguistic functions supported by Broca's area. Functional connectivity is thought to be achieved via corticothalamic/thalamocortical white matter pathways. Our study investigates structural connectivity between Broca's area and the thalamus, specifically ventral anterior nucleus and pulvinar. We demonstrate that Broca's area shares direct connections with these thalamic nuclei and suggest a local Broca's area-thalamus network potentially involved in linguistic processing. Thalamic connectivity with Broca's area may serve to selectively recruit cortical regions storing multimodal features of lexical items and to bind them together during lexical-semantic processing. In addition, Broca's area-thalamic circuitry may enable cortico-thalamo-cortical information transfer and modulation between BA 44 and 45 during language comprehension and production.

Aphasia or Neglect after Thalamic Stroke: The Various Ways They may be Related to Cortical Hypoperfusion

Although aphasia and hemispatial neglect are classically labeled as cortical deficits, language deficits or hemispatial neglect following lesions to subcortical regions have been reported in many studies. However, whether or not aphasia and hemispatial neglect can be caused by subcortical lesions alone has been a matter of controversy. It has been previously shown that most cases of aphasia or hemispatial neglect due to acute non-thalamic subcortical infarcts can be accounted for by concurrent cortical hypoperfusion due to arterial stenosis or occlusion, reversible by restoring blood flow to the cortex. In this study, we evaluated whether aphasia or neglect occur after acute thalamic infarct without cortical hypoperfusion due to arterial stenosis or occlusion. Twenty patients with isolated acute thalamic infarcts (10 right and 10 left) underwent MRI scanning and detailed cognitive testing. Results revealed that 5/10 patients with left thalamic infarcts had aphasia and only 1 had cortical hypoperfusion, whereas 2/10 patients with right thalamic infarcts had hemispatial neglect and both had cortical hypoperfusion. These findings indicate that aphasia was observed in some cases of isolated left thalamic infarcts without cortical hypoerfusion due to arterial stenosis or occlusion (measured with time-to-peak delays), but neglect occurred after isolated right thalamic infarcts only when there was cortical hypoperfusion due to arterial stenosis or occlusion. Therefore, neglect after acute right thalamic infarct should trigger evaluation for cortical hypoperfusion that might improve with restoration of blood flow. Further investigation in a larger group of patients and with other imaging modalities is warranted to confirm these findings.

Associative learning beyond the medial temporal lobe: many actors on the memory stage

Decades of research have established a model that includes the medial temporal lobe, and particularly the hippocampus, as a critical node for episodic memory. Neuroimaging and clinical studies have shown the involvement of additional cortical and subcortical regions. Among these areas, the thalamus, the retrosplenial cortex, and the prefrontal cortices have been consistently related to episodic memory performance. This article provides evidences that these areas are in different forms and degrees critical for human memory function rather than playing only an ancillary role. First we briefly summarize the functional architecture of the medial temporal lobe with respect to recognition memory and recall. We then focus on the clinical and neuroimaging evidence available on thalamo-prefrontal and thalamo-retrosplenial networks. The role of these networks in episodic memory has been considered secondary, partly because disruption of these areas does not always lead to severe impairments; to account for this evidence, we discuss methodological issues related to the investigation of these regions. We propose that these networks contribute differently to recognition memory and recall, and also that the memory stage of their contribution shows specificity to encoding or retrieval in recall tasks. We note that the same mechanisms may be in force when humans perform non-episodic tasks, e.g., semantic retrieval and mental time travel. Functional disturbance of these networks is related to cognitive impairments not only in neurological disorders, but also in psychiatric medical conditions, such as schizophrenia. Finally we discuss possible mechanisms for the contribution of these areas to memory, including regulation of oscillatory rhythms and long-term potentiation. We conclude that integrity of the thalamo-frontal and the thalamo-retrosplenial networks is necessary for the manifold features of episodic memory.

Training verb argument structure production in agrammatic aphasia: behavioral and neural recovery patterns

INTRODUCTION

Neuroimaging and lesion studies indicate a left hemisphere network for verb and verb argument structure processing, involving both frontal and temporoparietal brain regions. Although their verb comprehension is generally unimpaired, it is well known that individuals with agrammatic aphasia often present with verb production deficits, characterized by an argument structure complexity hierarchy, indicating faulty access to argument structure representations for production and integration into syntactic contexts. Recovery of verb processing in agrammatism, however, has received little attention and no studies have examined the neural mechanisms associated with improved verb and argument structure processing. In the present study we trained agrammatic individuals on verbs with complex argument structure in sentence contexts and examined generalization to verbs with less complex argument structure. The neural substrates of improved verb production were examined using functional magnetic resonance imaging (fMRI).

METHODS

Eight individuals with chronic agrammatic aphasia participated in the study (four experimental and four control participants). Production of three-argument verbs in active sentences was trained using a sentence generation task emphasizing the verb's argument structure and the thematic roles of sentential noun phrases. Before and after training, production of trained and untrained verbs was tested in naming and sentence production and fMRI scans were obtained, using an action naming task.

RESULTS

Significant pre- to post-training improvement in trained and untrained (one- and two-argument) verbs was found for treated, but not control, participants, with between-group differences found for verb naming, production of verbs in sentences, and production of argument structure. fMRI activation derived from post-treatment compared to pre-treatment scans revealed upregulation in cortical regions implicated for verb and argument structure processing in healthy controls.

CONCLUSIONS

Training verb deficits emphasizing argument structure and thematic role mapping is effective for improving verb and sentence production and results in recruitment of neural networks engaged for verb and argument structure processing in healthy individuals.

White matter structural connectivity underlying semantic processing: evidence from brain damaged patients

Widely distributed brain regions in temporal, parietal and frontal cortex have been found to be involved in semantic processing, but the anatomical connections supporting the semantic system are not well understood. In a group of 76 right-handed brain-damaged patients, we tested the relationship between the integrity of major white matter tracts and the presence of semantic deficits. The integrity of white matter tracts was measured by percentage of lesion voxels obtained in structural imaging and mean fractional anisotropy values obtained in diffusion tensor imaging. Semantic deficits were assessed by jointly considering the performance on three semantic tasks that vary in the modalities of input (visual and auditory stimuli) and output (oral naming and associative judgement). We found that the lesion volume and fractional anisotropy value of the left inferior fronto-occipital fasciculus, left anterior thalamic radiation, and left uncinate fasciculus significantly correlated with severity of impairment in all three semantic tasks. These associations remained significant even when we controlled for a wide range of potential confounding variables, including overall cognitive state, whole lesion volume, or type of brain damage. The effects of these three white matter tracts could not be explained by potential involvement of relevant grey matter, and were (relatively) specific to object semantic processing, as no correlation with performance on non-object semantic control tasks (oral repetition and number processing tasks) was observed. These results underscore the causal role of left inferior fronto-occipital fasciculus, left anterior thalamic radiation, and left uncinate fasciculus in semantic processing, providing direct evidence for (part of) the anatomical skeleton of the semantic network.

Thalamic mechanisms in language: a reconsideration based on recent findings and concepts

Recent literature on thalamic aphasia and thalamic activity during neuroimaging is selectively reviewed followed by a consideration of recent anatomic and physiological findings regarding thalamic structure and functions. It is concluded that four related corticothalamic and/or thalamocortical mechanisms impact language processing: (1) selective engagement of task-relevant cortical areas in a heightened state of responsiveness in part through the nucleus reticularis (NR), (2) passing information from one cortical area to another through corticothalamo-cortical mechanisms, (3) sharpening the focus on task-relevant information through corticothalamo-cortical feedback mechanisms, and (4) selection of one language unit over another in the expression of a concept, accomplished in concert with basal ganglia loops. The relationship and interaction of these mechanisms is discussed and integrated with thalamic aphasia and neuroimaging data into a theory of thalamic functions in language.

Semantic memory retrieval circuit: role of pre-SMA, caudate, and thalamus

We propose that pre-supplementary motor area (pre-SMA)-thalamic interactions govern processes fundamental to semantic retrieval of an integrated object memory. At the onset of semantic retrieval, pre-SMA initiates electrical interactions between multiple cortical regions associated with semantic memory subsystems encodings as indexed by an increase in theta-band EEG power. This starts between 100-150 ms after stimulus presentation and is sustained throughout the task. We posit that this activity represents initiation of the object memory search, which continues in searching for an object memory. When the correct memory is retrieved, there is a high beta-band EEG power increase, which reflects communication between pre-SMA and thalamus, designates the end of the search process and resultant in object retrieval from multiple semantic memory subsystems. This high beta signal is also detected in cortical regions. This circuit is modulated by the caudate nuclei to facilitate correct and suppress incorrect target memories.

Functional imaging of the thalamus in language

Herein, the literature regarding functional imaging of the thalamus during language tasks is reviewed. Fifty studies met criteria for analysis. Two of the most common task paradigms associated with thalamic activation were generative tasks (e.g. word or sentence generation) and naming, though activation was also seen in tasks that involve lexical decision, reading and working memory. Typically, thalamic activation was seen bilaterally, left greater than right, along with activation in frontal and temporal cortical regions. Thalamic activation was seen with perceptually challenging tasks, though few studies rigorously correlated thalamic activation with measures of attention or task difficulty. The peaks of activation loci were seen in virtually all thalamic regions, with a bias towards left-sided and midline activation. These analyses suggest that the thalamus may be involved in processes that involve manipulations of lexical information, but point to the need for more systematic study of the thalamus using language tasks.

The Involvement of the Thalamus in Semantic Retrieval: A Clinical Group Study

There is increasing attention about the role of the thalamus in high cognitive functions, including memory. Although the bulk of the evidence refers to episodic memory, it was recently proposed that the mediodorsal (MD) and the centromedian–parafascicular (CM–Pf) nuclei of the thalamus may process general operations supporting memory performance, not only episodic memory. This perspective agrees with other recent fMRI findings on semantic retrieval in healthy participants. It can therefore be hypothesized that lesions to the MD and the CM–Pf impair semantic retrieval. In this study, 10 patients with focal ischemic lesions in the medial thalamus and 10 healthy controls matched for age, education, and verbal IQ performed a verbal semantic retrieval task. Patients were assigned to a target clinical group and a control clinical group based on lesion localization. Patients did not suffer from aphasia and performed in the range of controls in a categorization and a semantic association task. However, target patients performed poorer than healthy controls on semantic retrieval. The deficit was not because of higher distractibility but of an increased rate of false recall and, in some patients, of a considerably increased rate of misses. The latter deficit yielded a striking difference between the target and the control clinical groups and is consistent with anomia. Follow-up high-resolution structural scanning session in a subsample of patients revealed that lesions in the CM–Pf and MD were primarily associated with semantic retrieval deficits. We conclude that integrity of the MD and the CM–Pf is required for semantic retrieval, possibly because of their role in the activation of phonological representations.

Semantic association fMRI impairments represent a potential schizophrenia biomarker

Semantic association retrieval task (SORT) requires participants to indicate whether word pairs recall a third object, e.g. 'honey' and 'stings' activates 'bees'. We have previously shown that individuals with schizophrenia with more severe positive symptoms tend to report associations between unrelated word pairs than healthy controls; schizophrenia individuals with more severe negative symptoms tend to fail to report associations between related word pairs. This over-retrieval and under-retrieval on SORT correlates with functional magnetic resonance imaging (fMRI) activity in inferior parietal lobule (IPL). To examine the suitability of SORT as an endophenotype for schizophrenia, we examined SORT performance and activity across multiple stages of the illness: chronic, relapse, and first episode. We also examine SORT performance and activity in unaffected relatives. SORT performance and fMRI activity in schizophrenia-first episode, schizophrenia-chronic and schizophrenia-relapse were significantly impaired relative to healthy controls and unaffected relatives. Schizophrenia-chronic and schizophrenia-relapse participants showing more severe PANSS-positive and -general symptoms showed larger SORT impairments. For schizophrenia-first episode more severe negative symptoms were related to lower IPL activation, consistent with previous results showing that negative symptoms are among the first to emerge in the schizophrenia prodrome and that more severe symptoms in the first episode predict worse future outcomes. Unaffected relatives showed no impairments on SORT performance or fMRI activity relative to healthy controls, which is incompatible with the concept of SORT as an endophenotype for schizophrenia, but is consistent with the concept of SORT as a potential schizophrenia biomarker.

Impairment in semantic retrieval is associated with symptoms in schizophrenia but not bipolar disorder

BACKGROUND

The Semantic Object Retrieval Task (SORT) requires participants to indicate whether word pairs recall a third object. Schizophrenia individuals (SZ) tend to report associations between nonassociated word pairs; this overretrieval is related to formal thought disorder (FTD). Since semantic memory impairments and psychosis are also found in bipolar disorder (BP), we examined whether SORT impairments and their relationship to symptoms are also present in BP.

METHODS

Participants (n = 239; healthy control subjects [HC] = 133; BP = 32; SZ = 74) completed SORT while undergoing functional magnetic resonance imaging (fMRI) scanning.

RESULTS

Retrieval accuracy negatively correlated with negative symptoms and no-retrieval accuracy negatively correlated with FTD severity in SZ but not BP. Retrieval versus no-retrieval trials activated a distributed fronto-parieto-temporal network; bilateral inferior parietal lobule (IPL) activity was larger in HC versus SZ and HC versus BP, with no difference in SZ versus BP. Right IPL activity positively correlated with positive and general psychosis symptoms in SZ but not BP.

CONCLUSIONS

SZ reported more associations between unrelated word pairs than HC; this overretrieval increased with FTD severity. Schizophrenia individuals were also more likely to fail to find associations between related word pairs; this underretrieval increased with negative symptom severity. fMRI symptom correlations in IPL in SZ are consistent with arguments that IPL abnormality relates to loosening of associations in SZ. By comparison, BP showed intermediate impairments on SORT, uncorrelated with symptoms, suggesting that the relationship between SORT performance, fMRI activity, and psychotic symptoms is schizophrenia-specific.

Comparing implicit and explicit semantic access of direct and indirect word pairs in schizophrenia to evaluate models of semantic memory

Semantic memory deficits in schizophrenia (SZ) are profound, yet there is no research comparing implicit and explicit semantic processing in the same participant sample. In the current study, both implicit and explicit priming are investigated using direct (LION-TIGER) and indirect (LION-STRIPES; where tiger is not displayed) stimuli comparing SZ to healthy controls. Based on a substantive review (Rossell and Stefanovic, 2007) and meta-analysis (Pomarol-Clotet et al., 2008), it was predicted that SZ would be associated with increased indirect priming implicitly. Further, it was predicted that SZ would be associated with abnormal indirect priming explicitly, replicating earlier work (Assaf et al., 2006). No specific hypotheses were made for implicit direct priming due to the heterogeneity of the literature. It was hypothesised that explicit direct priming would be intact based on the structured nature of this task. The pattern of results suggests (1) intact reaction time (RT) and error performance implicitly in the face of abnormal direct priming and (2) impaired RT and error performance explicitly. This pattern confirms general findings regarding implicit/explicit memory impairments in SZ whilst highlighting the unique pattern of performance specific to semantic priming. Finally, priming performance is discussed in relation to thought disorder and length of illness.

Using ketamine to model semantic deficits in schizophrenia

Semantic deficits constitute a core cognitive abnormality in schizophrenia. In the current study, the N-methyl-d-aspartate receptor antagonist ketamine was administered to healthy individuals acutely while they performed semantic processing tasks that included word pairs of differing degrees of semantic relatedness. Two dimensions of semantic processing were investigated: (1) explicit versus implicit processing, that is, unconscious versus conscious processing of semantic relationships and (2) direct versus indirect processing, that is, word pairs that are closely (LION-TIGER) or distantly (LION-STRIPES) related. The immediate effects of ketamine (0.8 mg/kg per hour during 80 minutes with approximate target plasma levels of 200 ng/mL) were examined in a placebo-controlled double-blind repeated-measures group design with 19 participants. It was predicted that ketamine would disrupt access to semantic memory as evidenced in schizophrenia, especially the indirectly related word pairs. In addition, implicit processing and explicit processing were predicted to be differentially affected. Ketamine administration did result in an abnormal performance in the reaction time responses to implicitly presented indirectly related word pairs (ie, greater priming) and reduced accuracy for explicit pairs. Performance on the directly related word pair tasks (both implicit and explicit) was similar across ketamine and placebo conditions, except for the suggestion of abnormal semantic matching in the accuracy data in the implicit task. This study confirms that implicit indirect semantic processing is changed under the influences of ketamine akin to schizophrenia. Future research comparing a schizophrenia group and a ketamine group directly about these tasks is needed to determine the similarity of impairments.

The neuroanatomic correlates of semantic memory deficits in patients with Gulf War illnesses: a pilot study

We used functional magnetic resonance imaging (fMRI) to study semantic memory processing in 38 Gulf War veterans in 3 affected groups (Syndromes 1, 2, and 3) and normal-deployed controls. Subjects were given the Semantic Object Retrieval Test (SORT), which requires participants to decide whether two features combine and result in the retrieval of a specific object (e.g., "desert" and "humps" → "camel"). Differences between groups were calculated using a repeated measures analysis of variance (ANOVA). Then, regions of interest were constructed and correlations assessed between the percent signal change (PSC) within these regions, followed by correlations between behavioral measures and PSC. We found affected groups performed less well on the SORT than the controls did, and behavioral differences were correlated to PSC within the caudate and thalamus. The combination of performance deficits and functional neuroimaging differences between affected Gulf War veterans and deployed normal controls begins to establish a neurobiological basis for their word-finding deficits.

Subjective report of word-finding and memory deficits in normal aging and dementia

OBJECTIVE

Compare subjective reports of both memory and word-finding deficits to clinical diagnosis and objective neuropsychological testing.

BACKGROUND

With the increasing number of aging individuals with cognitive impairments, effective screening measures would improve the likelihood of detection. Subjective reports of symptoms are typically obtained in clinical settings, yet the validity of these reports is relatively unknown.

METHODS

Clinical screening for dementia was carried out at an Alzheimer disease center. Dichotomous ratings for memory and word-finding/language problems were given by patients and neurologists. These ratings were compared with 13 neuropsychological measures of word-finding/language and episodic memory.

RESULTS

Ratings of memory by both patients and neurologists correlated well with standard neuropsychological measures of memory. However, both the patients' and physicians' ratings of word-finding/language impairments had notably less of a correlation with the relevant neuropsychological measures of word-finding/language.

CONCLUSION

Compared with ratings of memory, similar assessments of word-finding/language difficulties were relatively inaccurate, and thus poor predictors of impairment. It is imperative to develop effective screening methods that will help reveal cognitive impairments, as this issue will almost certainly become more pressing given the projected increase in the number of aging individuals and those with dementia.

Broad and narrow conceptual tuning in the human frontal lobes

Previous work has implicated prefrontal cortices in selecting among and retrieving conceptual information stored elsewhere. However, recent neurophysiological work in monkeys suggests that prefrontal cortex may play a more direct role in representing conceptual information in a flexible context-specific manner. Here, we investigate the nature of visual object representations from perceptual to conceptual levels in an unbiased data-driven manner using a functional magnetic resonance imaging adaptation paradigm with pictures of animals. Throughout much of occipital cortex, activity was highly sensitive to changes in 2D stimulus form, consistent with tuning to form and position within retinotopic coordinates and matching an automated measure of shape similarity. Broad superordinate conceptual information was represented as early as extrastriate and posterior ventral temporal cortex. These regions were not completely invariant to form, suggesting that form similarity remains an important organizational constraint into the temporal cortex. Separate sites within prefrontal cortex represented broad and narrow conceptual tuning, with more anterior sites tuned narrowly to close conceptual associates in a manner that was invariant to stimulus form/position and that matched independent similarity ratings of the stimuli. The combination of broad and narrow conceptual tuning within prefrontal cortex may support flexible selection, retrieval, and classification of objects at different levels of categorical abstraction.

A semantic model to study neural organization of language in bilingualism

A neural network model of object semantic representation is used to simulate learning of new words from a foreign language. The network consists of feature areas, devoted to description of object properties, and a lexical area, devoted to words representation. Neurons in the feature areas are implemented as Wilson-Cowan oscillators, to allow segmentation of different simultaneous objects via gamma-band synchronization. Excitatory synapses among neurons in the feature and lexical areas are learned, during a training phase, via a Hebbian rule. In this work, we first assume that some words in the first language (L1) and the corresponding object representations are initially learned during a preliminary training phase. Subsequently, second-language (L2) words are learned by simultaneously presenting the new word together with the L1 one. A competitive mechanism between the two words is also implemented by the use of inhibitory interneurons. Simulations show that, after a weak training, the L2 word allows retrieval of the object properties but requires engagement of the first language. Conversely, after a prolonged training, the L2 word becomes able to retrieve object per se. In this case, a conflict between words can occur, requiring a higher-level decision mechanism.

Functional Neuroanatomy of Contextual Acquisition of Concrete and Abstract Words

The meaning of a novel word can be acquired by extracting it from linguistic context. Here we simulated word learning of new words associated to concrete and abstract concepts in a variant of the human simulation paradigm that provided linguistic context information in order to characterize the brain systems involved. Native speakers of Spanish read pairs of sentences in order to derive the meaning of a new word that appeared in the terminal position of the sentences. fMRI revealed that learning the meaning associated to concrete and abstract new words was qualitatively different and recruited similar brain regions as the processing of real concrete and abstract words. In particular, learning of new concrete words selectively boosted the activation of the ventral anterior fusiform gyrus, a region driven by imageability, which has previously been implicated in the processing of concrete words.

Syllable congruency and word frequency effects on brain activation

This article investigates the neural representation of the processes involved in recognizing multisyllabic words in Spanish asking whether lexical and sublexical processes are reflected in a different neuronal activation pattern. High and low frequency words were presented for lexical decision in two different colors. In the congruent condition the color boundaries matched the limit of the first syllable, whereas in the incongruent condition color boundaries and syllable boundaries did not match. The results revealed robust and dissociable brain activations for lexical frequency and syllable-color congruency, but no interaction between the two. We interpreted the greater activation for low relative to high frequency words in the left pre/SMA region, and in the insula/inferior frontal cortex bilaterally to reflect a differential recruitment of lexico-phonological and/or semantic processes. In contrast, we considered two interpretations for the greater deactivation in the precuneus for both lexical frequency and syllable-color congruency words, and in the thalami and a frontal area for syllable-color congruency words only. The deactivations may reflect the differential engagement of semantic processing or may result from the differential allocation of attentional resources. Importantly, while a differential deactivation pattern was observed in the precuneus region for lexicality and syllable-color congruency, BOLD deconvolution revealed a remarkable difference in timing of the two effects with a much earlier deactivation peak for the syllable-color congruency factor. Thus, effects of lexical frequency and syllable-color congruency on brain activation show an important dissociation between lexical and sublexical processes during visual word recognition of multisyllabic words.

Temporal sequence of hemispheric network activation during semantic processing: a functional network connectivity analysis

To explore the temporal sequence of, and the relationship between, the left and right hemispheres (LH and RH) during semantic memory (SM) processing we identified the neural networks involved in the performance of functional MRI semantic object retrieval task (SORT) using group independent component analysis (ICA) in 47 healthy individuals. SORT requires participants to determine whether word pairs describing object features combine to retrieve an object. Functional network connectivity (FNC) was used to assess the correlations between components' time courses. Results showed that semantic left and right hemisphere networks comprise two independent ICA components. The components' time courses were highly correlated and RH activation preceded that of the LH. Moreover, this correlation was significantly stronger in better vs. poorer performers of the SORT. These results indicate an early activation of the RH that is closely followed by activation of the LH, to facilitate performance during word retrieval from SM.

A neural network model of semantic memory linking feature-based object representation and words

Recent theories in cognitive neuroscience suggest that semantic memory is a distributed process, which involves many cortical areas and is based on a multimodal representation of objects. The aim of this work is to extend a previous model of object representation to realize a semantic memory, in which sensory-motor representations of objects are linked with words. The model assumes that each object is described as a collection of features, coded in different cortical areas via a topological organization. Features in different objects are segmented via gamma-band synchronization of neural oscillators. The feature areas are further connected with a lexical area, devoted to the representation of words. Synapses among the feature areas, and among the lexical area and the feature areas are trained via a time-dependent Hebbian rule, during a period in which individual objects are presented together with the corresponding words. Simulation results demonstrate that, during the retrieval phase, the network can deal with the simultaneous presence of objects (from sensory-motor inputs) and words (from acoustic inputs), can correctly associate objects with words and segment objects even in the presence of incomplete information. Moreover, the network can realize some semantic links among words representing objects with shared features. These results support the idea that semantic memory can be described as an integrated process, whose content is retrieved by the co-activation of different multimodal regions. In perspective, extended versions of this model may be used to test conceptual theories, and to provide a quantitative assessment of existing data (for instance concerning patients with neural deficits).

Brain mechanisms of persuasion: how 'expert power' modulates memory and attitudes

Human behaviour is affected by various forms of persuasion. The general persuasive effect of high expertise of the communicator, often referred to as 'expert power', is well documented. We found that a single exposure to a combination of an expert and an object leads to a long-lasting positive effect on memory for and attitude towards the object. Using functional magnetic resonance imaging, we probed the neural processes predicting these behavioural effects. Expert context was associated with distributed left-lateralized brain activity in prefrontal and temporal cortices related to active semantic elaboration. Furthermore, experts enhanced subsequent memory effects in the medial temporal lobe (i.e. in hippocampus and parahippocampal gyrus) involved in memory formation. Experts also affected subsequent attitude effects in the caudate nucleus involved in trustful behaviour, reward processing and learning. These results may suggest that the persuasive effect of experts is mediated by modulation of caudate activity resulting in a re-evaluation of the object in terms of its perceived value. Results extend our view of the functional role of the dorsal striatum in social interaction and enable us to make the first steps toward a neuroscientific model of persuasion.

Functional Neuroanatomy of Meaning Acquisition from Context

An important issue in language learning is how new words are integrated in the brain representations that sustain language processing. To identify the brain regions involved in meaning acquisition and word learning, we conducted a functional magnetic resonance imaging study. Young participants were required to deduce the meaning of a novel word presented within increasingly constrained sentence contexts that were read silently during the scanning session. Inconsistent contexts were also presented in which no meaning could be assigned to the novel word. Participants showed meaning acquisition in the consistent but not in the inconsistent condition. A distributed brain network was identified comprising the left anterior inferior frontal gyrus (BA 45), the middle temporal gyrus (BA 21), the parahippocampal gyrus, and several subcortical structures (the thalamus and the striatum). Drawing on previous neuroimaging evidence, we tentatively identify the roles of these brain areas in the retrieval, selection, and encoding of the meaning.

Language performance in Alzheimer's disease and mild cognitive impairment: a comparative review

Mild cognitive impairment (MCI) manifests as memory impairment in the absence of dementia and progresses to Alzheimer's disease (AD) at a rate of around 15% per annum, versus 1-2% in the general population. It thus constitutes a primary target for investigation of early markers of AD. Language deficits occur early in AD, and performance on verbal tasks is an important diagnostic criterion for both AD and MCI. We review language performance in MCI, compare these findings to those seen in AD, and identify the primary issues in understanding language performance in MCI and selecting tasks with diagnostic and prognostic value.

Event-related potentials in semantic memory retrieval

The involvement of the left temporal lobe in semantics and object naming has been repeatedly demonstrated in the context of language comprehension; however, its role in the mechanisms and time course for the retrieval of an integrated object memory from its constituent features have not been well delineated. In this study, 19 young adults were presented with two features of an object (e.g., "desert" and "humps") and asked to determine whether these two features were congruent to form a retrieval of a specific object ("camel") or incongruent and formed no retrieval while event-related potentials (ERP) were recorded. Beginning around 750 ms the ERP retrieval and nonretrieval waveforms over the left anterior fronto-temporal region show significance differences, indicating distinct processes for retrievals and nonretrievals. In addition to providing further data implicating the left frontal-anterior temporal region in object memory/retrieval, the results provide insight into the time course of semantic processing related to object memory retrieval in this region. The likely semantic process at 750 ms in this task would be coactivation of feature representations common to the same object. The consistency of this finding suggests that the process is stable across individuals. The potential clinical applications are discussed.

The subcortical role of language processing. High level linguistic features such as ambiguity-resolution and the human brain; an fMRI study

In the present study, we were interested in the neurofunctional representations of ambiguity processing by using functional magnetic resonance imaging (fMRI). Twelve right-handed, healthy adults aged between 21 and 29 years (6 male, 6 female) underwent an ambiguity resolution task with 4 different conditions (dominant vs. non-dominant; dominant vs. distractor; non-dominant vs. distractor; distractor vs. distractor). After subtraction of the corresponding control task (distractor vs. distractor) we found significant activation especially in the thalamus and some parts of the basal ganglia (caudate nucleus, putamen). Our findings implicate a participation of the thalamus and other basal ganglia circuits in high level linguistic functions and match with theoretical considerations on this highly controversial topic. Subcortical neural circuits probably become activated when the language processing system cannot rely entirely on automatic mechanisms but has to recruit controlled processes as well. Furthermore, we found broad activation in the inferior parietal lobule, the prefrontal gyrus, pre-SMA and SMA and the cingulate cortex. This might reflect a strategic semantic search mechanism which probably can be illustrated with connectionist models of language processing. According to this, we hypothesize a neuroregulatory role for the thalamus and basal ganglia in regulating and monitoring the release of preformulated language segments for motor programming and semantic verification. According to our findings there is strong evidence, that especially the thalamus, the caudate nucleus, the cingulate cortex, the inferior parietal lobule and the prefrontal cortex are responsible for an accurate ambiguity resolution in the human brain.

Neural substrates of semantic memory

Semantic memory is described as the storage of knowledge, concepts, and information that is common and relatively consistent across individuals (e.g., memory of what is a cup). These memories are stored in multiple sensorimotor modalities and cognitive systems throughout the brain (e.g., how a cup is held and manipulated, the texture of a cup's surface, its shape, its function, that is related to beverages such as coffee, and so on). Our ability to engage in purposeful interactions with our environment is dependent on the ability to understand the meaning and significance of the objects and actions around us that are stored in semantic memory. Theories of the neural basis of the semantic memory of objects have produced sophisticated models that have incorporated to varying degrees the results of cognitive and neural investigations. The models are grouped into those that are (1) cognitive models, where the neural data are used to reveal dissociations in semantic memory after a brain lesion occurs; (2) models that incorporate both cognitive and neuroanatomical information; and (3) models that use cognitive, neuroanatomic, and neurophysiological data. This review highlights the advances and issues that have emerged from these models and points to future directions that provide opportunities to extend these models. The models of object memory generally describe how category and/or feature representations encode for object memory, and the semantic operations engaged in object processing. The incorporation of data derived from multiple modalities of investigation can lead to detailed neural specifications of semantic memory organization. The addition of neurophysiological data can potentially provide further elaboration of models to include semantic neural mechanisms. Future directions should incorporate available and newly developed techniques to better inform the neural underpinning of semantic memory models.

Neuropsychological deficits after bithalamic hemorrhages

Strategic lesions of the thalamus interfere with cognitive functions and produce complex neuropsychological symptoms. Bilateral, simultaneous thalamic hemorrhages are unusual causes of thalamic dementia. We present clinical, neuropsychological and structural neuroimaging data of a 12-month follow-up period of a patient with bilateral thalamic hemorrhages. After the operation of pancreatitis acuta hemorrhagico-necroticans, the patient developed coma. Computed tomography (CT) and magnetic resonance (MR) of the brain showed medially situated bithalamic hematomas. During the follow-up period, patient's level of consciousness has improved. Moderate dementia (MMSE 20/30) was found with severe temporal and spatial disorientation. Neuropsychological tests showed that attention and concentration were prominently impaired; there were severe verbal and less prominent, visual memory deficits, with anterograde and retrograde amnesia, accompanied by confabulations. Loss of cognitive flexibility and dysexecutive syndrome were also demonstrated. Dynamic apraxia, visual organization and visual construction deficit and impairment of categorial and phonemic fluency were noted. Language was only moderately impaired (anomia). A year later, neuropsychological profile was similar with moderate improvement of retrograde amnesia, whereas anterograde deficits persisted. Neuropsychological syndrome in our patient with bilateral thalamic hemorrhages was characteristic for subcortico-cortical cognitive deficit and was caused by disruption of the cortico-thalamic circuitry.