Frontal lobe dysfunction following infarction of the left-sided medial thalamus

Restraint stress-induced effects on learning, memory, cognition, and expression of transcripts in different brain regions of mice

BACKGROUND

Stress is one of the prevalent factors influencing cognition. Several studies examined the effect of mild or chronic stress on cognition. However, most of these studies are limited to a few behavioral tests or the expression of selected RNA/proteins markers in a selected brain region.

METHODS

This study examined the effect of restraint stress on learning, memory, cognition, and expression of transcripts in key learning centers. Male mice were divided into three groups (n = 6/group)-control group, stress group (adult stressed group; S), and F1 group (parental stressed group). Stress group mice were subjected to physical restraint stress for 2 h before light offset for 2 weeks. The F1 group comprised adult male mice born of stressed parents. All animals were subjected to different tests and were sacrificed at the end. Transcription levels of Brain-Derived Neurotrophic Factor (Bdnf), Tyrosine kinase (TrkB), Growth Associated Protein 43 (Gap-43), Neurogranin (Ng), cAMP Response Element-Binding Protein (Creb), Glycogen synthase kinase-3β (Gsk3β), Interleukine-1 (IL-1) and Tumour necrosis factor-α (Tnf-α) were studied.

RESULTS

Results show that both adult and parental stress negatively affect learning, memory and cognition, as reflected by taking longer time to achieve the task or showing reduced exploratory behavior. Expression of Bdnf, TrkB, Gsk3β and Ng was downregulated, while IL-1 and Tnf-α were upregulated in the brain's cortex, thalamus, and hippocampus region of stressed mice. These effects seem to be relatively less severe in the offspring of stressed parents.

CONCLUSIONS

The findings suggest that physical restraint stress can alter learning, memory, cognition, and expression of transcripts in key learning centers of brain.

Subcortical Aphasia

PURPOSE OF REVIEW

Subcortical structures have long been thought to play a role in language processing. Increasingly spirited debates on language studies, arising from as early as the nineteenth century, grew remarkably sophisticated as the years pass. In the context of non-thalamic aphasia, a few theoretical frameworks have been laid out. The disconnection hypothesis postulates that basal ganglia insults result in aphasia due to a rupture of connectivity between Broca and Wernicke's areas. A second viewpoint conjectures that the basal ganglia would more directly partake in language processing, and a third stream proclaims that aphasia would stem from cortical deafferentation. On the other hand, thalamic aphasia is more predominantly deemed as a resultant of diaschisis. This article reviews the above topics with recent findings on deep brain stimulation, neurophysiology, and aphasiology.

RECENT FINDINGS

The more recent approach conceptualizes non-thalamic aphasias as the offspring of unpredictable cortical hypoperfusion. Regarding the thalamus, there is mounting evidence now pointing to leading contributions of the pulvinar/lateral posterior nucleus and the anterior/ventral anterior thalamus to language disturbances. While the former appears to relate to lexical-semantic indiscrimination, the latter seems to bring about a severe breakdown in word selection and/or spontaneous top-down lexical-semantic operations. The characterization of subcortical aphasias and the role of the basal ganglia and thalamus in language processing continues to pose a challenge. Neuroimaging studies have pointed a path forward, and we believe that more recent methods such as tractography and connectivity studies will significantly expand our knowledge in this particular area of aphasiology.

Thalamocortical Functional Connectivity in Patients With White Matter Hyperintensities

Background: White matter hyperintensities (WMH)s is a very common neuroradiological manifestation in the elderly and is an increased risk of dementia and cognitive decline. As we all know, the thalamocortical circuit plays an important part in cognition regulation. However, the role of this circuit in WMHs and its related cognitive deficits is still unclear.

Method: Eighty WMH patients and 37 healthy controls (HCs) were enrolled in the current study. WMH patients were divided into a mild WMH group (n = 33) and moderate-severe WMH group (n = 47) according to Fazekas scores. Resting-state functional magnetic resonance imaging (rs-fMRI) data of all participants were collected for thalamocortical functional connectivity (FC) analysis. The analysis was performed in two steps. First, the whole cerebral cortex was divided into six regions of interest (ROIs), which were used as seeds to investigate the changes of FC with the thalamus. Then, the subregion of the thalamus generated in the previous step was used as the seed for FC analysis with the whole brain.

Results: In the first step of FC analysis, it was found that precentral gyrus (PrCG)-interthalamic adhesion (ITA) FC values in moderate-severe WMH group were higher than those in HC and mild WMH groups. However, when compared with the HC group, the increase of PrCG-ITA FC values in mild WMH group was not statistically significant. In the second step of FC analysis, the ITA was set as the seed, and compared with the HC group, the results showed that the FC values of the ITA-medial frontal gyrus (MFG) in mild group and moderate-severe WMH groups were significantly increased. In addition, the FC values in moderate-severe group were significantly higher than those in mild group. Finally, it was also found that FC values (PrCG-ITA and ITA-MFG) were significantly correlated with neuropsychological test results for multiple cognitive functions such as memory, execution and attention in WMH patients.

Conclusion: Abnormal thalamocortical FC was closely related with cognitive impairments in WMH patients.

A Multimodal Imaging Study in a Case of Bilateral Thalamic Damage With Multidomain Cognitive Impairment

Severe thalamic injury can determine a particular type of vascular dementia affecting multiple network dysfunctions, considered the central role of thalamus as a hub for afferent and efferent stimuli. A 67-year-old male patient with bilateral thalamic stroke was studied with positron emission tomography, magnetic resonance imaging, and cognitive assessment, performed at baseline and at two follow-up evaluations. A pattern primarily involving thalamo-frontal connections was observed by both PET and tractography analyses. All significant differences between the patient and controls involved the anterior thalamic radiation, one of the major fiber tracts in the fronto-thalamic circuitry. In particular, altered tractography indices of higher radial diffusivity and apparent diffusion coefficient and reduced fractional anisotropy values for the anterior thalamic radiation were reported. In accordance with imaging findings, neuropsychological evaluation demonstrated a multidomain impairment including memory, executive functions, and attention. Additionally, the patients displayed behavioral symptoms, in absence of mood alterations. Multimodal imaging assessment, revealing the metabolic and microstructural alterations that attend to multidomain neuropsychological impairment, demonstrated multiple levels of adaptations to bilateral vascular thalamic injury.

Gender and Hemispheric Asymmetries in Acquired Sociopathy

The emergence of enduring antisocial personality changes in previously normal individuals, or "acquired sociopathy," has consistently been reported in patients with bilateral injuries of the ventromedial prefrontal cortex. Over the past three decades, cases of acquired sociopathy with (a) bilateral or (b) unilateral sparing of the ventromedial prefrontal cortex have been reported. These cases indicate that at least in a few individuals (a') neural structures beyond the ventromedial prefrontal cortex are also critical for normal social behavior, and (b') the neural underpinnings of social cognition may be lateralized to one cerebral hemisphere. Moreover, researchers have presented evidence that lesion laterality and gender may interact in the production of acquired sociopathy. In the present review, we carried out a comprehensive literature survey seeking possible interactions between gender and hemispheric asymmetry in acquired sociopathy. We found 85 cases of acquired sociopathy due to bilateral (N = 48) and unilateral (N = 37) hemispheric injuries. A significant association between acquired sociopathy and right hemisphere damage was found in men, whereas lesions were bilateral in most women with acquired sociopathy. The present survey shows that: (i) the number of well-documented single-cases of acquired sociopathy is surprisingly small given the length of the historical record; (ii) acquired sociopathy was significantly more frequent in men after an injury of the right or of both cerebral hemispheres; and (iii) in most women who developed acquired sociopathy the injuries affected both cerebral hemispheres. These findings may be especially valuable to neuroscientists and to functional neurosurgeons in particular for the planning of tumor resections as well as for the choice of the best targets for therapeutic neuromodulation.

Lesion location and cognitive impact of cerebral small vessel disease

Cerebral small vessel disease (SVD) is an important cause of cognitive impairment. Important MRI manifestations of SVD include white matter hyperintensities (WMH) and lacunes. This narrative review addresses the role of anatomical lesion location in the impact of SVD on cognition, integrating findings from early autopsy studies with emerging findings from recent studies with advanced image analysis techniques. Early autopsy and imaging studies of small case series indicate that single lacunar infarcts in, for example the thalamus, caudate nucleus or internal capsule can cause marked cognitive impairment. However, the findings of such case studies may not be generalizable. Emerging location-based image analysis approaches are now being applied to large cohorts. Recent studies show that WMH burden in strategic white matter tracts, such as the forceps minor or anterior thalamic radiation (ATR), is more relevant in explaining variance in cognitive functioning than global WMH volume. These findings suggest that the future diagnostic work-up of memory clinic patients could potentially be improved by shifting from a global assessment of WMH and lacune burden towards a quantitative assessment of lesion volumes within strategic brain regions. In this review, a summary of currently known strategic regions for SVD-related cognitive impairment is provided, highlighting recent technical developments in SVD research. The potential and challenges of location-based approaches for diagnostic purposes in clinical practice are discussed, along with their potential prognostic and therapeutic applications.

Deep Brain Stimulation of Medial Dorsal and Ventral Anterior Nucleus of the Thalamus in OCD: A Retrospective Case Series

BACKGROUND

The current notion that cortico-striato-thalamo-cortical circuits are involved in the pathophysiology of obsessive-compulsive disorder (OCD) has instigated the search for the most suitable target for deep brain stimulation (DBS). However, despite extensive research, uncertainty about the ideal target remains with many structures being underexplored. The aim of this report is to address a new target for DBS, the medial dorsal (MD) and the ventral anterior (VA) nucleus of the thalamus, which has thus far received little attention in the treatment of OCD.

METHODS

In this retrospective trial, four patients (three female, one male) aged 31-48 years, suffering from therapy-refractory OCD underwent high-frequency DBS of the MD and VA. In two patients (de novo group) the thalamus was chosen as a primary target for DBS, whereas in two patients (rescue DBS group) lead implantation was performed in a rescue DBS attempt following unsuccessful primary stimulation.

RESULTS

Continuous thalamic stimulation yielded no significant improvement in OCD symptom severity. Over the course of thalamic DBS symptoms improved in only one patient who showed "partial response" on the Yale-Brown Obsessive Compulsive (Y-BOCS) Scale. Beck Depression Inventory scores dropped by around 46% in the de novo group; anxiety symptoms improved by up to 34%. In the de novo DBS group no effect of DBS on anxiety and mood was observable.

CONCLUSION

MD/VA-DBS yielded no adequate alleviation of therapy-refractory OCD, the overall strategy in targeting MD/VA as described in this paper can thus not be recommended in DBS for OCD. The magnocellular portion of MD (MDMC), however, might prove a promising target in the treatment of mood related and anxiety disorders.

Memory Profiles after Unilateral Paramedian Thalamic Stroke Infarction: A Comparative Study

We performed extensive neuropsychological assessment of two male patients (matched for age and educational level) with similar (localization and size) unilateral paramedian ischemic thalamic lesions (AB on the left and SD on the right). Both patients showed severe memory impairments as well as other cognitive deficits. In comparison to SD, AB showed severe impairment of executive functions and a more severe deficit of episodic/anterograde memory, especially in the verbal modality. The findings of this single case study suggest the possibility that the profile and severity of the executive dysfunction are determinant for the memory deficits and depend on from the side of the lesion. In addition to a material-side-specific (verbal versus visual) deficit hypothesis, the differential diencephalo-prefrontal contributions in mnestic-processing, in case of paramedian thalamic stroke, might also be explained in terms of their stage-specificity (encoding versus retrieval).

Social cognition in Alzheimer's disease: a separate construct contributing to dependence

The extent to which social cognitive changes reflect a discrete constellation of symptoms dissociable from general cognitive changes in Alzheimer's disease (AD) is unclear. Moreover, whether social cognitive symptoms contribute to disease severity and progression is unknown. The current multicenter study investigated cross-sectional and longitudinal associations between social cognition measured with six items from the Blessed Dementia Rating Scale, general cognition, and dependence in 517 participants with probable AD. Participants were monitored every 6 months for 5.5 years. Results from multivariate latent growth curve models adjusted for sex, age, education, depression, and recruitment site revealed that social cognition and general cognition were unrelated cross-sectionally and throughout time. However, baseline levels of each were related independently to dependence, and change values of each were related independently to change in dependence. These findings highlight the separability of social and general cognition in AD. Results underscore the relevance of considering social cognition when modeling disease and estimating clinical outcomes related to patient disability.

Damage to the dorsomedial thalamic nucleus, central lateral intralaminar thalamic nucleus, and midline thalamic nuclei on the right-side impair executive function and attention under conditions of high demand but not low demand

This study reports a patient, OG, with a unilateral right-sided thalamic lesion. High resolution 3T magnetic resonance imaging revealed damage to the parvicellular and magnocellular subdivisions of the dorsomedial thalamus (DMT), the central lateral intralaminar nucleus (also known as the paralamellar DMT), the paraventricular and the central medial midline thalamic nuclei. According to the neuropsychological literature, the DMT, the midline and intralaminar thalamic nuclei influence a wide array of cognitive functions by virtue of their modulatory influences on executive function and attention, and this is particularly indicated under conditions of low arousal or high cognitive demand. We explored this prediction in OG, and compared his performance on a range of low and high demand versions of tests that tapped executive function and attention to a group of 6 age- and IQ-matched controls. OG, without exception, significantly under performed on the high-demand attention and executive function tasks, but performed normally on the low-demand versions. These findings extend and refine current understanding of the effects of thalamic lesion on attention and executive function.

Explorations of object and location memory using fMRI

Content-specific sub-systems of visual working memory (VWM) have been explored in many neuroimaging studies with inconsistent findings and procedures across experiments. The present study employed functional magnetic resonance imaging (fMRI) and a change detection task using a high number of trials and matched stimulus displays across object and location change (what vs. where) conditions. Furthermore, individual task periods were studied independently across conditions to identify differences corresponding to each task period. Importantly, this combination of task controls has not previously been described in the fMRI literature. Composite results revealed differential frontoparietal activation during each task period. A separation of object and location conditions yielded a distributed system of dorsal and ventral streams during the encoding of information corresponding to bilateral inferior parietal lobule (IPL) and lingual gyrus activation, respectively. Differential activity was also shown during the maintenance of information in middle frontal structures bilaterally for objects and the right IPL and left insula for locations. Together, these results reflect a domain-specific dissociation spanning several cortices and task periods. Furthermore, differential activations suggest a general caudal-rostral separation corresponding to object and location memory, respectively.

The medial dorsal thalamic nucleus and the medial prefrontal cortex of the rat function together to support associative recognition and recency but not item recognition

In humans recognition memory deficits, a typical feature of diencephalic amnesia, have been tentatively linked to mediodorsal thalamic nucleus (MD) damage. Animal studies have occasionally investigated the role of the MD in single-item recognition, but have not systematically analyzed its involvement in other recognition memory processes. In Experiment 1 rats with bilateral excitotoxic lesions in the MD or the medial prefrontal cortex (mPFC) were tested in tasks that assessed single-item recognition (novel object preference), associative recognition memory (object-in-place), and recency discrimination (recency memory task). Experiment 2 examined the functional importance of the interactions between the MD and mPFC using disconnection techniques. Unilateral excitotoxic lesions were placed in both the MD and the mPFC in either the same (MD + mPFC Ipsi) or opposite hemispheres (MD + mPFC Contra group). Bilateral lesions in the MD or mPFC impaired object-in-place and recency memory tasks, but had no effect on novel object preference. In Experiment 2 the MD + mPFC Contra group was significantly impaired in the object-in-place and recency memory tasks compared with the MD + mPFC Ipsi group, but novel object preference was intact. Thus, connections between the MD and mPFC are critical for recognition memory when the discriminations involve associative or recency information. However, the rodent MD is not necessary for single-item recognition memory.

The Neurocognitive Phenotype of Apathy following Acquired Brain Damage

Apathy is one of the most common neuropsychiatric sequelae of acquired brain damage. The disorder is usually defined in terms of observed deficits in motivation related behavioural, emotional, and cognitive aspects of goal directed activity. Most neuropsychological research on apathy has focused primarily on its associated neurocognitive correlates; particularly those related to executive dysfunction, or its association with other clinical syndromes like depression. Results from these studies have been mixed, probably reflecting the use of different neuropsychiatric samples and assessment tools, or reflecting the differences in the conceptualisation of apathy across studies. In this study we ask whether performance on ‘standard’ executive tests would distinguish brain-damaged patients with apathy symptoms from those without apathy. To potentially strengthen the power of the possible relationships between apathy and executive function we included brain-injured patients with varied aetiologies, and used a much broader range of ‘executive function’ tests than in previous studies. Results indicate that the Tower of Hanoi puzzle is sensitive to apathy symptoms. Patients with apathy symptoms were significantly impaired on the task compared to non-apathetic patients. Performance on the Wisconsin Card Sorting test, the Hayling and Brixton tests, and the Stroop test failed to show this distinction. We discuss these findings and their implications for treatment and rehabilitation.

Focal brain atrophy in gastric bypass patients with cognitive complaints

Recently, we have identified a series of patients presenting with cognitive complaints after gastric bypass, without any identifiable etiology. We aimed to determine if focal brain atrophy could account for the complaints. A retrospective case series was performed to identify patients with cognitive complaints following gastric bypass who had a volumetric MRI. Voxel-based morphometry was used to assess patterns of grey matter loss in all 10 patients identified, compared to 10 age and gender-matched controls. All patients had undergone Roux-en-Y gastric bypass surgery at a median age of 54 (range: 46-64). Cognitive complaints developed at a median age of 57 (52-69). Formal neuropsychometric testing revealed only minor deficits. No nutritional abnormalities were identified. Voxel-based morphometry demonstrated focal thalamic atrophy in the gastric bypass patients when compared to controls. Patients with cognitive complaints after gastric bypass surgery may have focal thalamic brain atrophy that could result in cognitive impairment.

WITHDRAWN: fMRI correlates of visual working memory: What vs. where

This article has been withdrawn at the request of the authors. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy. This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Working memory in 8 Kleine-Levin syndrome patients: an fMRI study

STUDY OBJECTIVES

The objectives of this study were to investigate possible neuropathology behind the Kleine-Levin Syndrome (KLS), a severe form of hypersomnia with onset during adolescence.

DESIGN

Functional magnetic resonance imaging (fMRI) applying a verbal working memory task was used in conjunction with a paper-and-pencil version of the task.

PARTICIPANTS

Eight patients with KLS and 12 healthy volunteers participated in the study.

RESULTS

The results revealed a pattern of increased thalamic activity and reduced frontal activity (involving the anterior cingulate and adjacent prefrontal cortex) while performing a reading span task.

DISCUSSION

This finding may explain the clinical symptoms observed in KLS, in that the thalamus is known to be involved in the control of sleep. Given the increasing access to fMRI, this investigation may aid clinicians in the diagnosis of patients suffering from severe forms of hypersomnia.

Thalamofrontal circuitry and executive dysfunction in recent-onset juvenile myoclonic epilepsy

PURPOSE

Thalamofrontal abnormalities have been identified in chronic primary generalized epilepsy, specifically in juvenile myoclonic epilepsy (JME). These regions also underlie executive functioning, although their relationship has yet to be examined in JME. This study examined the relationship between thalamic and frontal volumes and executive function in recent-onset JME compared to healthy control subjects and recent-onset benign childhood epilepsy with centrotemporal spikes (BCECTS), a syndrome not typically associated with thalamocortical or executive dysfunction.

METHODS

Twenty children with recent-onset JME were compared to 51 healthy controls and 12 children with BCECTS using quantitative magnetic resonance imaging (MRI) and measures of executive abilities. Quantitative thalamic and frontal volumes were obtained through semi-automated software. Subtests from the Delis-Kaplan Executive Function System (D-KEFS) and the Behavior Rating Inventory of Executive Function (BRIEF) were used to measure executive function.

RESULTS

Executive functions were impaired in JME subjects compared to control and BCECTS subjects. Subjects with JME had significantly smaller thalamic volumes and more frontal cerebrospinal fluid (CSF) than control and BCECTS subjects. Thalamic and frontal volumes were significantly related to executive functioning in the JME group, but not in the other two groups.

DISCUSSION

Children with JME have significant executive dysfunction associated with significantly smaller thalami and more frontal CSF. Children with recent-onset BCECTS do not display the same pattern. Frontal and thalamic volumes appear to mediate the relationship between executive functioning and brain structure in JME.

The Human Thalamus is Crucially Involved in Executive Control Operations

The processing of executive control is thought to involve cortical as well as thalamic brain areas. However, the questions of how thalamic structures contribute to the control of behavior and how cortical versus thalamic processing is coordinated remain to be settled. We therefore aimed at specifying respective activations during the performance of a go/no-go task. To this end, an electroencephalogram was recorded simultaneously from scalp and thalamic electrodes in seven patients undergoing deep brain stimulation. Meanwhile, left- or right-directed precues were presented indicating with which index finger a button press should be putatively executed. Thereafter, 2 sec elapsed until a go or no-go stimulus determined if the prepared movement had to be performed or withheld. In fronto-central scalp as well as in thalamic recordings, event-related potentials upon go versus no-go instructions were expressed differentially. This task effect was unrelated to motor processes and emerged significantly prior at thalamic than at scalp level. Amplitude fluctuations of depth and scalp responses showed site- and task-dependent correlations, particularly between thalamic and no-go-related activities at frontal recording sites. We conclude that an early classification of go and no-go instructions is performed already thalamically. It further appears that this information is subsequently utilized by cortical areas engaged in the definite inhibition of the prepared action.

Construct Validity of the Wisconsin Card Sorting Test-64 in Patients with Stroke

This study examined the factor structure and contrasted-group validity of the Wisconsin Card Sorting Test-64 (WCST-64) in a stroke sample (n = 112). Confirmatory factor analyses were used to compare five different models suggested by prior factor analyses. The results indicated that the WCST-64 was best represented by a three-dimensional model comprising response inflexibility (factor 1), ineffective hypothesis-testing strategy (factor 2), and set maintenance (factor 3). A significant overall multivariate effect for group (F = 2.87, df = 18,495.46, p <.001) was found in a multivariate analysis of covariance with WCST scores as dependent variables and four different groups (three stroke subgroups with different levels of cognitive function and a normal control group) as independent variable, after controlling for gender. The results of discriminant analysis supported the use of the WCST-64 in stroke patients with cognitive impairment.

Frontal-subcortical circuitry and behavior

The neuropsychiatric manifestations of neurodegenerative diseases are closely linked to neurocircuitry defects. Frontal-subcortical circuits, in particular, are effector mechanisms that allow the organism to act on its environment In this paper, we present the three main frontal-subcortical circuits: the dorsolateral prefrontal circuit allows the organization of information to facilitate a response; the anterior cingulate circuit is required for motivated behavior; and the orbitofrontal circuit allows the integration of limbic and emotional information into behavioral responses. Impaired executive functions, apathy, and impulsivity are hallmarks of frontal-subcortical circuit dysfunction. A variety of other neuropsychiatrie disorders, such as Tourette's syndrome, Huntington's disease, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, schizophrenia, and mood disorders may result from disturbances that have a direct or indirect impact on the integrity or functioning of these loops.

Secondary mania of vascular origin in elderly patients: A report of two clinical cases

The concept of secondary mania continues to be debated together with unresolved or partially resolved issues such as lateralization, localization, age of onset, disinhibition syndromes, and others. We have described two patients with secondary mania following a stroke. One had a large left hemisphere cerebral infarction and the symptoms arose about 2.5 years later, possibly triggered by a transient ischemic attack involving the right hemisphere. The other had an infarction in the right posterior artery territory extending to the thalamus and internal capsule together with infarctions in the deep border zones of both hemispheres at the level of the centrum semiovale with the manic symptoms concomitant with the onset of the event. The clinical and neuro-anatomic mechanisms that underlie the diverse locations of secondary mania are discussed. The cerebral components of secondary mania and disinhibition syndromes are very similar and it is proposed that disinhibition syndromes, secondary hypomania and secondary mania with and without psychotic symptoms are simply a continuum of severity of mood disorder and secondary mania with psychotic symptoms may be an extreme form. The concept of secondary mania in the elderly is not likely to disappear although several unresolved issues remain. For the neurophysician, geriatrician, and the psychiatrist there is much to be attained by simplifying the issues and accepting the view that secondary mania is a discrete entity.

Hypersexuality following bilateral thalamic infarction: case report

Hypersexuality is a rare but well recognized condition following brain injury. It has been described secondarily to dysfunction in the hypothalamus, the temporal and frontal lobes. We report a 63 year-old man that developed neuropsychological disturbances with hypersexuality as a prominent feature, disinhibition and moderate memory loss, hypersomnia and irritability after a bilateral paramedian thalamic infarction. A SPECT showed frontal hypoperfusion. We believe that these findings are expression of frontal-subcortical circuits dysfunction, particularly the orbitofrontal circuit, secondary to dorso medial thalamic infarction which probably plays a role in the determination of human sexual behavior. This case favors a thalamic modulation of frontal function.

Thalamic Lesions in Vascular Dementia

BACKGROUND AND PURPOSE

The criteria of the National Institute of Neurological Disorders and Stroke (NINDS)-Association Internationale pour la Recherche et l'Enseignement en Neurosciences (AIREN) include thalamic lesions for the diagnosis of vascular dementia (VaD). Although studies concerning VaD and brain aging advocate the use of fluid-attenuated inversion recovery (FLAIR) or T2-weighted images (T2-WI) to detect ischemic lesions, none compared the sensitivity of these sequences to depict thalamic lesions.

METHODS

We performed a blinded review of T2-WI and FLAIR images in 73 patients fulfilling the radiological part of the NINDS-AIREN criteria (mean age, 71 years; range, 49 to 83 years). This sample was drawn from a large multicenter trial on VaD and was expected to have a high prevalence of thalamic lesions. In a side-by-side review, including T1-weighted images as well, lesions were classified according to presumed underlying pathology.

RESULTS

The total number of thalamic lesions was 214. Two hundred eight (97%) were detected on T2-WI, but only 117 (55%) were detected on FLAIR (chi(2)=5.1; P<0.05). Although the mean size of lesions detected on T2-WI and not on FLAIR (4.4 mm) was significantly lower than the mean size of lesions detected on both sequences (6.7 mm) (P<0.001), 5 of the 29 lesions >10 mm on T2-WI were not visible on FLAIR. FLAIR detected only 81 (51%) of the 158 probable ischemic lesions and 30 (60%) of the 50 probable microbleeds.

CONCLUSIONS

FLAIR should not be used as the only T2-weighted sequence to detect thalamic lesions in patients suspected of having VaD.

MRI correlates of executive dysfunction in patients with ischaemic stroke

Executive dysfunction (ED) may lead to problem behaviour and impaired activities of daily living in many neuropsychiatric disorders, but the neuroanatomical correlates of ED are still not well known. Different aspects of executive functions were studied by widely used neuropsychological tests in 214 elderly patients 3 months after ischaemic stroke, and a sum score of eight different measures was counted in each patient. The number and site of brain infarcts as well as severity and location of white matter lesions (WMLs) and brain atrophy on magnetic resonance imaging were recorded and compared between patients with and without ED. ED was present in 73 (34.1%) of the 214 patients. The mean frequency of brain infarcts in the brain and in the left hemisphere was higher in the patients with ED. Lesions affecting the frontal-subcortical circuits (e.g. pallidum, corona radiata or centrum semiovale) were more frequent in patients with ED than in those without. Also, patients with pontine brain infarcts frequently had ED, but this may have been due to more extensive ischaemic changes in these patients in general. Mean number of brain infarcts affecting the pons and posterior centrum semiovale on the left side, moderate to severe medial temporal atrophy, the Fazekas white matter score, the Mini-Mental State Examination score and low education were independent correlates of ED. Brain infarcts and WML affecting the frontal-subcortical circuits or the pons may increase risk for ED in stroke patients.

Frontal lobe dysfunction caused by multiple lacunar infarction in community-dwelling elderly subjects

We examined the factors that influence frontal lobe function among 119 community-dwelling elderly subjects, based on magnetic resonance imaging (MRI) and clinical findings. We interviewed the subjects, and conducted a neurological examination, electrocardiogram, blood test, brain MRI examination, and cognitive function tests. The modified Stroop test and a personal computer version of the Wisconsin Card Sorting Test (WCST) were used to evaluate frontal lobe function. The subjects with impaired frontal lobe function defined by the modified Stroop test were significantly older, had more lacunar infarcts, and had lower HDL cholesterol values based on a logistic regression model. Among the aged who appear apparently normal, multiple lacunar infarcts are the cause of latent frontal lobe dysfunction.

Deficits of memory, executive functioning and attention following infarction in the thalamus; a study of 22 cases with localised lesions

The thalamus plays a crucial role in memory, executive functioning and attention. It remains, however, unclear whether thalamic structures have specific roles in each of these functions. We tested 22 cases of thalamic infarction, proven with MR imaging, using experimental and established neuropsychological tests. We performed a lesion-overlap study in standardised stereotactic space of patients sharing a certain deficit, corrected for the lesion distribution of patients without such deficits and determined the regions of interest using an atlas of the human thalamus. We checked for additional, non-thalamic, damage and for deficient comprehension and perception that would preclude interpretation of the results. Non-thalamic damage such as white matter lesions, hippocampal atrophy, sulcal widening and infarctions occur significantly more often in patients aged over 60. The patients with additional damage overlapped to a major degree with those who showed loss of orientation, or lack of comprehension of the test requirements. In the 10 patients judged 'clean', we observed a deficit of episodic long-term memory with relative sparing of intellectual capacities and short-term memory when the mammillo-thalamic tract was damaged. Lesions including the medial dorsal nucleus, midline nuclei and/or intralaminar nuclei accompany executive dysfunctioning. Reduced simple processing speed and attention are associated with age, but not with a particular structure in the thalamus. Complex attention deficits follow damage to the intralaminar nuclei.We conclude that the analysis of structure-function relationships must take into account extra-structure damage which may explain cognitive deficits. Separate thalamic structures are involved in memory, executive functioning and attention.

Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions and ablations in humans

Since the mid-1960s, essentially using electrophysiological methods, our research group has examined the effects of different brain diseases in humans, both on first- and second-order conditioned responses and on some types of neurocognitive potentials of the CNV complex. This didactic lecture will focus on our various attempts to identify and understand the neuroanatomical and neurophysiological substrates involved in cognitive information processing followed by the conception and execution of sensory-motor and behavioural responses evoked by significant acoustic stimuli, in both pathological situations and normal control subjects. Great interest was, e.g. aroused in the early 1970s by the rare, fortunately unrepeatable, opportunity of examining the CNV patterns in various psychiatric patients treated with psychosurgical Freeman-Watts bilateral prefrontal 'radical' lobotomy, also with repeated recordings (The Responsive Brain (1976) 158; Multidisciplinary Perspectives in Event-Related Brain-Potentials Research (1978) 376) or bimedial bifrontal cingulotomy (Multidisciplinary Perspectives in Event-Related Brain Potential Research (1978) 383). In the same period, investigations into CNV activity recorded in patients submitted to complete callosotomy ('split brain': Attention and Performance, vol. IV (1972) 221; Electroenceph. Clin. Neurophysiol. Suppl. 33 (1973) 161) were also begun and were continued into the 1980s, also with regard to other types of ERP (Brain 111 (1988) 553; J. Cog. Neurosci. 2 (1990) 258). All these data furnished unique information about the sub-second dynamics of unilateral or bihemispheric cortico-cortical and cortico-subcortical interconnections in humans. In recent years, with a classic method of analysis based on sequential scalp-topographic bidimensional neuroelectric mapping and 21/19 electrodes connected to three different references, and binaural/monaural clicks as warning signals (S1), we have repeatedly examined the CNV activity of 11 selected patients submitted to complete ablation of the damaged cortical areas, with uni- or bilateral lesions restricted to the prefrontal or associative parieto-temporal areas. We have always used the standard CNV paradigm (S1-S2 motor-response) which evokes a complex of neurocognitive potentials, including the P300 from S1, which are well-known, since they are certainly among the most studied ERPs in the various ages and races of normal subjects, psychiatric patients and subjects with different brain diseases. The most important results have been, (1) In normal subjects the MRI and the latency differences of CNV component measurements along the bidirectional pathways functionally interconnecting ipsilateral distant associative cortical areas (e.g. the arcuate-superior longitudinal complex bundle) were accounted for by the transcortical conduction time, which varies in our scalp recordings from 1 cm/0.74 to 1.28 ms ( approximately 9.8 m/s). (2) Constantly, no true auditory S1-elicited N1a, b, c, P2, N2, P300 components or CNV slow waves (O- and E-wave) were recordable over the whole of the ablated cortical areas, but only clearly identifiable volume-conducted EP/ERPs generated in other hemispheric structures. (3) The post-S1 ERP/CNV complexes on the intact hemisphere were found to be within the normal limits. (4) Effects of severe disruption on the S1 ERP/CNV complexes evocable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions were observed in 5 patients, 4 of whom had extensive frontocortical ablations. In two of the latter the distant disruptive action on the CNV components over the neuroradiologically normal ipsilateral two-way connected post-rolandic sensory and association areas was seen to be partially reversible, showing aspects of a probable slowly evolving diaschisis-like effect. Similar deactivation of some ERP components was observed in reverse on the ipsilateral dorsolateral frontocortical region in the fifth patient with a large parieto-temporal cortex ablation. These data require confirmahese data require confirmation, and when this phenomenon is observable, it must be appropriately monitored with different methods of functional neuroimaging. This will serve not only for medical and neuropsychophysiological diagnosis purposes, but also particularly for a correct and really useful planning of neuro-rehabilitation activities in selected cases.

Screaming, shrieking and muttering: the noise-makers amongst dementia patients

We have described twelve dementia patients with noise making. We categorized noise making into (i) persistent screaming, (ii) perseverative vocalization, (iii) continuous chattering, muttering, singing or humming, and (iv) swearing, grunting and bizarre noise-making. The patients' ages ranged from 70 to 92 years with a mean of 78. There were four males and eight females. Five had Alzheimer's disease and the remaining seven vascular dementia. Five exhibited mild to moderate aggression while another five displayed severe aggression. All but one had motor restlessness and four had delusions or hallucinations. In ten patients the dementia was moderate to severe with five having total dissolution of speech. All but two were in the third stage of the illness and were totally dependent for basic self care. There was a wide network of anatomical structures involved in the twelve patients. The findings are related to what is known of the neuroanatomic location of the lesions and the role of frontal subcortical circuitry and neurotransmitter systems in relation to behavior. Noise-making could be explained by damage to the frontal lobe or interruption of the complex subcortical circuits and related brain chemistry. Treatment of patients with noise-making remains a challenge.

Thalamus and language: interface with attention, memory and executive functions

Subcortical structures are in a strategic functional position within the cognitive networks. Their lesion can interfere with a great number of functions. We studied six patients with thalamic vascular lesions (three left sided, two right sided and one bilateral), to characterize their repercussion in the communicative abilities and the interface between language alterations and other cognitive abilities, as attention, memory and frontal executive. All patients were evaluated through a functional interview (discourse analysis), and the following batteries: Boston Diagnostic Aphasia Examination, Boston Naming Test, Token Test, Benton Visual Retention Test, Trail Making, Wisconsin Card Sorting and frontal scripts. All patients performed MRI and five underwent SPECT. Results show that these patients present impairment in several cognitive domains, especially attention and executive functions (working memory, planning and self-monitoring); those with right lesions have an additional visuospatial impairment. Such alterations interfere with language abilities, and this fact must be considered in the rehabilitation efforts.

Neuropsychological manifestations in a case of bilateral thalamic infarction

Neuropsychological manifestation has been reported with lesions of the anterior and non-specific thalamic nuclei and mammilothalamic tract (MMT). These have been reported in the setting of arterial infarction and/or haemorrhage. Cerebral venous sinus thrombosis (CVT) is a rare cause of brain infarction. It occurs in the setting of oral contraceptive administration or pregnancy. Inherited thrombophilias are documented risk factors. The most frequent being heterozygous factor V Leiden mutation. We report a single case of bilateral thalamic infarction due to cerebral vein and sinus thrombosis. Clinically the case manifested with memory impairment and dysexecutive symptoms. Predisposing factor for venous thrombosis was a homozygous factor V Leiden mutation. The patient was treated with anticoagulation and made a good recovery.

The cerebral correlates of set-shifting: an fMRI study of the trail making test

The trail making test (TMT) pertains to a family of tests that tap the ability to alternate between cognitive categories. However, the value of the TMT as a localizing instrument remains elusive. Here we report the results of a functional magnetic resonance imaging (fMRI) study of a verbal adaptation of the TMT (vTMT). The vTMT takes advantage of the set-shifting properties of the TMT and, at the same time, minimizes the visuospatial and visuomotor components of the written TMT. Whole brain BOLD fMRI was performed during the alternating execution of vTMTA and vTMTB in seven normal adults with more than 12 years of formal education. Brain activation related to the set-shifting component of vTMTB was investigated by comparing performance on vTMTB with vTMTA, a simple counting task. There was a marked asymmetry of activation in favor of the left hemisphere, most notably in dorsolateral prefrontal cortex (BA 6 lateral, 44 and 46) and supplementary motor area/cingulate sulcus (BA 6 medial and 32). The intraparietal sulcus (BA 7 and 39) was bilaterally activated. These findings are in line with clinico-anatomic and functional neuroimaging data that point to a critical role of the dorsolateral and medial prefrontal cortices as well as the intraparietal sulci in the regulation of cognitive flexibility, intention, and the covert execution of saccades/anti-saccades. Many commonly used neuropsychological paradigms, such as the Stroop, Wisconsin Card Sorting, and go - no go tasks, share some patterns of cerebral activation with the TMT.

Frontal and parieto-temporal cortical ablations and diaschisis-like effects on auditory neurocognitive potentials evocable from apparently intact ipsilateral association areas in humans: five case reports

The aim of this study was to investigate the effects of disruption on the warning auditory S1-elicited ERP and CNV complexes recordable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions. These effects in some cases showed aspects of a probable diaschisis-like phenomenon, due to resections of extensive frontal association cortex or of primary and secondary sensory parieto-temporal areas damaged by differing pathological processes. Using a standard CNV paradigm, 21/19 EEG electrodes connected with three different references, and scalp-topographic bidimensional mapping analysis, the S1 auditory binaural/monaural clicks N1a,b,c, P2, N2, P3 and CNV waves were recorded in 10 normal subjects and 11 patients. Nine of the latter had been submitted to unilateral frontal dorsolateral cortex ablation, one to bihemispheric dorsomedial cortex ablation, and one to unilateral ablation of sensory parieto-temporal cortex and underlying white matter, verified through CT/MRI examinations. No true S1ERP/CNV components were recordable over the ablated cortical areas, whereas normal ERP/CNV complexes were observable on the intact hemispheres. In five patients, four of whom with frontocortical ablations, the S1 ERP/CNV complexes appeared severely diminished or disrupted, in two cases in a slow, partially-reversible manner, also in the neuroradiologically normal ipsilateral functionally-connected post-rolandic sensory and association areas. Similar deactivation of some ERP components was observed in reverse on the unilateral dorsolateral frontocortical region in the fifth patient with parieto-temporal cortex ablation. Even when they are partially reversible, these ipsilateral remote ERP changes in apparently intact brain regions, due to ablations of functionally-interconnected cortical formations, probably reflect cortical deactivation or simply dysfacilitation deriving from functional unilateral diaschisis. If these changes are instead irreversible they may probably be interpreted as transneuronal degeneration phenomena, though they are not at present easy to document either neuroradiologically or electroclinically.

Dissociation of mechanisms underlying syllogistic reasoning

A key question for cognitive theories of reasoning is whether logical reasoning is inherently a sentential linguistic process or a process requiring spatial manipulation and search. We addressed this question in an event-related fMRI study of syllogistic reasoning, using sentences with and without semantic content. Our findings indicate involvement of two dissociable networks in deductive reasoning. During content-based reasoning a left hemisphere temporal system was recruited. By contrast, a formally identical reasoning task, which lacked semantic content, activated a parietal system. The two systems share common components in bilateral basal ganglia nuclei, right cerebellum, bilateral fusiform gyri, and left prefrontal cortex. We conclude that syllogistic reasoning is implemented in two distinct systems whose engagement is primarily a function of the presence or absence of semantic content. Furthermore, when a logical argument results in a belief-logic conflict, the nature of the reasoning process is changed by recruitment of the right prefrontal cortex.

Effects of centrolateral or medial thalamic lesions on motor coordination and spatial orientation in rats

The effects of central lateral (CL) or medial thalamic lesions were evaluated on tests requiring balance and equilibrium (rotorod, stationary beam, and hole-board), and spatial orientation (Morris water maze). Lesions of the medial nuclei impaired rotorod and spatial orientation, while CL lesions impaired only rotorod performance. Neither lesion affected stationary beam and hole-board tests or visuomotor guidance while swimming toward a visible platform. These spatial and sensorimotor deficits cannot be explained by reduced cerebral activation, but instead are attributable to specific projections from the anterior intralaminar nuclei to the basal ganglia and neocortex.

Loss of psychic self-activation after paramedian bithalamic infarction

BACKGROUND AND PURPOSE

Loss of psychic self-activation has been described after bilateral lesions to the globus pallidus, striatum, and white matter of the frontal lobes, but it is a very rare sign of bithalamic lesions. The exact functional-anatomic mechanism underlying loss of psychic self-activation following bithalamic lesions remains to be elucidated.

CASE DESCRIPTION

We present clinical, neuropsychological, structural, and functional neuroimaging data of an 18-month follow-up period of a man with prominent loss of psychic self-activation after coronary arteriography. Except for memory decline, accompanying symptoms remained restricted to the acute phase. The neurobehavioral syndrome consisted mainly of apathy, indifference, poor motivation, and flattened affect, and this remained unchanged during the entire follow-up period. MRI showed a bithalamic infarction involving the nucleus medialis thalami bilaterally. Single-photon emission CT revealed a severe relative hypoperfusion of both thalami, a relative hypoperfusion of both nuclei caudati, and a relative hypoperfusion mesiofrontally.

CONCLUSIONS

Single-photon emission CT data support the hypothesis that the neurobehavioral manifestations after bithalamic paramedian infarction are caused by disruption of the striatal-ventral pallidal-thalamic-frontomesial limbic loop. Probably, bilateral disruption at different levels of the striatal-ventral pallidal-thalamic-frontomesial loop may lead to a similar clinical picture consisting of loss of psychic self-activation.

Role of dopamine in learning and memory: implications for the treatment of cognitive dysfunction in patients with Parkinson's disease

Along with dementia, Parkinson's disease (PD) is associated with subtle but widespread cognitive impairment even in the absence of clinically apparent cognitive decline. Many of the deficits are reminiscent of those observed in patients with lesions of the prefrontal cortex, that is, failure in executive function that involves skills required for anticipation, planning, initiation and monitoring of goal-directed behaviours. This paper reviews the dopaminergic brain circuitry, and preclinical and clinical evidence supporting the regulation of prefrontal cortex activity by dopamine, and the role of dopamine in cognitive impairment in patients with PD. It addresses the need to integrate these facts and the findings of positive, neutral or detrimental frontal cognitive response to dopaminergic drugs in PD which should be viewed mainly in the context of methodological differences for subject selection. The cognitive effect of levodopa does not much depend on a neuropsychological specificity of the drug, the years of evolution of the disease or the severity of the motor signs. Instead, it may be a function of the level of dopamine depletion in different parts of the basal ganglia and prefrontal cortex. Consequently, dopaminergic agents may enhance cognitive functions in some patients and impair them in others. De novo patients tend to improve during the first year of treatment; stable responders to oral levodopa tend to show no changes; and wearing-off responders tend to deteriorate with acute levodopa challenge. Enhancement and impairment of cognitive function with dopaminergic treatment is incomplete and task-specific, suggesting the need to integrate the above dopamine facts with other neurotransmitter systems findings in PD. Meanwhile, such cognitive dissociation can be useful in refining the definition of the cognitive deficit in PD patients without dementia and emphasising the need to develop new and specific strategies for treatment.

Neuropsychology of infarctions in the thalamus: a review

From a review of the literature on the consequences of thalamic infarctions, it may be concluded that memory problems taking the form of an amnesic syndrome are dependent upon the integrity of the mammillo-thalamic tract (MTT). Memory problems incompatible with an amnesic syndrome however, appear to result from thalamic infarctions involving other areas of the thalamus but which leave MTT intact. In contrast, executive dysfunctions could not be shown so readily to depend upon a single structure of the thalamus. The results indicate that damage to the mediodorsal nucleus of the thalamus, the midline nuclei or the intralaminar nuclei, or a combined lesion of these structures may be responsible for deficits of executive functioning.

Neuroimaging variables related to development of Secondary Attention Deficit Hyperactivity Disorder after closed head injury in children and adolescents

OBJECTIVE

To characterize children who develop Secondary Attention Deficit Hyperactivity Disorder (S-ADHD) after severe and moderate closed head injury (CHI) according to neuroimaging variables.

METHOD

Ninety-nine children from 4-19 years who suffered severe and moderate CHI were prospectively followed for a year after injury. Premorbid psychiatric status was determined by administration to the parent of a structured psychiatric interview. This interview was readministered 1 year after injury to determine the presence of post-closed head injury S-ADHD. An MRI was performed 3 months after injury to define lesion locations and volumes.

RESULTS

A set of multiple logistic regression models determined that the odds of developing S-ADHD were 3.64 times higher among children with thalamus injury, and 3.15 times higher among children with basal ganglia injury. There was no significant difference in lesion volumes in any of the locations of interest between the group who developed S-ADHD and the group who did not develop S-ADHD.

CONCLUSION

The data support an association between S-ADHD and injury in either or both the thalamus and basal ganglia, but they do not definitively demonstrate whether injury in either structure has an effect on S-ADHD in the absence of injury in the other.

Disorders of higher mental function due to single infarctions in the thalamus and in the area of the thalamofrontal tracts

Nine patients (five female and four male, mean age 58 years) with small infarcts in the thalamus (TH) or in the region of the thalamofrontal tracts and producing acute mental disturbances which in the acute phase of insult consisted of dementia in seven cases and mild cognitive disturbances in two cases. The complex of mental changes was similar to that seen in "frontal syndrome" and was characterized largely by lack of spontaneity, adynamia, disorientation, loss of attention and memory, slowing of all mental processes, and lack of criticality and adequacy. Accompanying focal neurological symptoms were mild in seven patients and moderate or pronounced in two. In five patients, the severity of mental disturbances decreased with time. Computer tomography demonstrated small infarcts in the anterior or medial parts of the TH in seven patients and in the posteromedial parts of the anterior limb of the internal capsule, i.e., the thalamofrontal tracts, in two cases. In five cases, infarcts were located in the dominant hemisphere, with lesions in the non-dominant hemisphere in three and in both hemispheres in one. The positions of all foci corresponded to structures traversed by pathways connecting the TH and the lower part of the reticular formation to the frontal lobes. It is suggested that disconnection of these pathways leads to cognitive lesions or dementia because of functional inactivation of the frontal cortex.

Akinetic mutism and mixed transcortical aphasia following left thalamo-mesencephalic infarction

A 54-year-old man developed somnolent akinetic mutism and acute mixed transcortical aphasia following a left thalamo-mesencephalic infarction. He also exhibited behavioural changes, namely apathy, slowness, lack of spontaneity, disinhibition, perseveration, gait apraxia and incontinence consistent with frontal lobe dysfunction. Presumably the akinetic mutism and language dysfunction were due to the thalamic stroke. All the manifestations could be related to interruption of the frontal-subcortical circuitry.

Neuropsychological correlates of a right unilateral lacunar thalamic infarction

OBJECTIVES

To report on a patient with a lacunar infarction in the right intralaminar nuclei of the thalamus. The role of the thalamic intralaminar nuclei in cognitive function is as yet insufficiently known. The patient described has shown signs of apathy and loss of initiative, in combination with cognitive deficits, which have persisted essentially unaltered up to the present day since an abrupt onset 17 years ago.

METHODS

High resolution MRI was performed to show the extent of the lesion; a combination of published and experimental neuropsychological techniques was administered to show the nature of the cognitive defects; Single photon emission computed tomography (SPECT) was employed to obtain a measure of cortical perfusion.

RESULTS

Brain MRI disclosed an isolated lacunar infarction in the dorsal caudal intralaminar nuclei of the thalamus. Neuropsychological evaluation indicated problems with attention and concentration, executive disturbances, and memory deficits both in the visual and verbal domains. The memory deficits could not be attributed to problems in the early stages of information processing, and are hence regarded as resulting from a failure of retrieval rather than encoding or storage. Brain SPECT disclosed a hypoperfusion of the right frontal cortex.

CONCLUSION

The data indicate that the cognitive profile is the result of a dysfunction of executive functions. This is corroborated by the finding of decreased blood flow in the right frontal cortex, and by evidence from the neuroanatomical literature. Thus the dysexecutive symptoms are thought to be caused by disconnection of the prefrontal cortex from the brainstem activating nuclei through the strategic localisation of the right thalamic infarction.

Diaschisis and neurobehavior

We review forms of diaschisis and their relationship with neurobehavioral and neuropsychological findings. The following forms of diaschisis are discussed: (1) cortico-cerebellar diaschisis; (2) cerebello-cortical diaschisis; (3) transhemispheric diaschisis; (4) cortico-thalamic diaschisis; (5) thalamo-cortical diaschisis; and (6) basal ganglia-cortical diaschisis. For each form, the neurobehavioral and neuropsychological findings are discussed. Diaschisis can be classified from the behavioral point of view as follows: (1) forms in which the metabolic effect at distance is not followed by neurobehavioral impairment; (2) forms in which the remote metabolic impairment could induce neurobehavioral and neuropsychological disorders; and (3) forms in which the role of the lesion itself and its remote metabolic effects on the production of neurobehavioral and neuropsychological abnormalities cannot be disentangled.

Subcortical aphasia

We critically review the literature on subcortical aphasia, suggest that a number of traditional concepts regarding mechanisms of aphasia are inconsistent with now abundant data, and propose several new hypotheses. The absence of aphasia in 17 reported cases of dominant hemisphere striatocapsular infarction and the finding of nearly every conceivable pattern of language impairment in 33 different reported cases of striatocapsular infarction provide strong evidence against a major direct role of the basal ganglia in language and against disconnection or diaschisis as mechanisms of nonthalamic subcortical aphasia. However, detailed consideration of the vascular events leading to striatocapsular infarction strongly suggests that associated linguistic deficits are predominantly related to sustained cortical hypoperfusion and infarction not visible on structural imaging studies. Thalamic disconnection, as may occur with striatocapsular infarcts with extension to the temporal stem and putamenal hemorrhages, may also contribute to the language deficits in some patients. Review of the literature on thalamic infarction, in conjunction with previously unreported anatomic details of four cases, suggests that what infarcts in the tuberothalamic artery territory and the occasional infarcts in the paramedian artery territory associated with aphasia have in common is damage to the frontal lobe-inferior thalamic peduncle-nucleus reticularis-center median system that may be involved in regulating the thalamic gate in attentional processes. Disruption of attentional gating in the pulvinar and lateral posterior nuclei resulting from such lesions may impair selection of specific neuronal networks in the projection field of these nuclei that serve as the substrate for lexical-semantic function, which is in effect a disruption of a type of working memory, as defined by Goldman-Rakic. We define this as a defect of selective engagement.

Functional Neuroimaging of Cortical Dysfunction in Alcoholic Korsakoff's Syndrome

Many neuropsychological investigations of human memory have focused on the amnesic deficits of alcoholic Korsakoff's syndrome. Structural neuroimaging suggests that the syndrome results from midline diencephalic damage, but functional neuroimaging has the potential to reveal additional neuropathology that may be responsible for cognitive dysfunction. Accordingly, high-resolution positron emission tomography (PET) was used to measure regional cerebral metabolic rates for glucose utilization in five alcoholic Korsakoff patients and nine alcoholic control subjects. Results from a continuous recognition test administered during the radiotracer uptake period indicated that all subjects performed normally with respect to immediate memory, whereas Korsakoff patients demonstrated a marked memory impairment in delayed recognition. PET results from the Korsakoff group showed a widespread decline in glucose metabolism in frontal, parietal, and cingulate regions, suggesting that these functional abnormalities in the cerebral cortex contribute to the memory impairment. Hippocampal glucose metabolism did not differ between the groups. Thus, the evidence did not support the hypothesis that parallel brain dysfunctions are responsible for the similar amnesic symptomatology after hippocampal and diencephalic damage. We hypothesize that the amnesic dysfunction of Korsakoff's syndrome depends on a disruption of thalamocortical interactions that mediate a function critical for normal memory storage.

Differential visuospatial dysfunction following striatal, frontal white matter, or posterior thalamic infarction

The present study investigated visuospatial functioning in 35 right-hand dominant patients with striatal, frontal white matter, or posterior thalamic infarction, in the right cerebral hemisphere. On tasks of visual detection and discrimination, the groups performed within normal limits and comparable to one another. On tasks of visual synthesis and spatial analysis, each group was significantly impaired, with greatest impairment following infarction of deep grey structures. Correlational analyses indicated that in the striatal and frontal white matter groups, visual synthesis and spatial analysis task performance were strongly correlated with performance on neuropsychological tests of executive control. This relationship was not observed in the posterior thalamic group. The results support the hypothesis of differential patterns of visuospatial performance depending on the anatomical locus of subcortical lesions. The findings are explained in terms of differing subcortical circuitry and suggest that multiple substrates mediate the sequelae of subcortical lesions.

Subcortical Structures and Neuropsychiatric Illness

Subcortical structures play an important role in modulating mood, drive, memory, executive functions, and cognitive timing. Subcortical structures are intimately linked with the frontal lobe and limbic system. Key subcortical structures regulating behavior include the caudate nucleus, the ventral striatum, the ventral pallidum, and the dorsomedial and reticular nuclei of the thalamus. Some degenerative diseases affect subcortical nuclear and white matter structures, causing involuntary movements and abnormal behavior. Primary psychiatric illnesses, such as obsessive-compulsive disorder, have been proposed to arise from dysfunction in the frontostriatal-thalamic circuits. The neuroanatomical and neurochemical organization of these subcortical systems mediating complex behaviors and the interactions between behavioral and motor systems are increasingly well understood. Undoubtedly, our newer understanding of subcortical systems will help us to unravel the pathophysiology of some neuropsychiatric disorders.

Persistent pure verbal amnesia and transient aphasia after left thalamic infarction

A 57-year-old right-handed man suffered persistent pure verbal amnesia (PPVA) and transient aphasia after left thalamic infarction. A neuroanatomical study with magnetic resonance imaging to identify the site of the lesion showed destruction of the internal medullary lamina (IML), mammillothalamic tract (MTT), the ventrolateral nucleus (VL) and the lower one-third of the medial nucleus. As regions critical for PPVA are unknown, we reviewed the cases of PPVA after left thalamic infarction reported in the literature. These suggest that confined destruction of the IML, MTT and VL in the left thalamus can produce PPVA.