Normal memory after damage to medial thalamus

Characterization of Behaviour and Remote Degeneration Following Thalamic Stroke in the Rat

Subcortical ischemic strokes are among the leading causes of cognitive impairment. Selective atrophy of remote brain regions connected to the infarct is thought to contribute to deterioration of cognitive functions. The mechanisms underlying this secondary degenerative process are incompletely understood, but are thought to include inflammation. We induce ischemia by unilateral injection of endothelin-I into the rat dorsomedial thalamic nucleus, which has defined reciprocal connections to the frontal cortex. We use a comprehensive test battery to probe for changes in behaviour, including executive functions. After a four-week recovery period, brain sections are stained with markers for degeneration, microglia, astrocytes and myelin. Degenerative processes are localized within the stroke core and along the full thalamocortical projection, which does not translate into measurable behavioural deficits. Significant microglia recruitment, astrogliosis or myelin loss along the axonal projection or within the frontal cortex cannot be detected. These findings indicate that critical effects of stroke-induced axonal degeneration may only be measurable beyond a threshold of stroke severity and/or follow a different time course. Further investigations are needed to clarify the impact of inflammation accompanying axonal degeneration on delayed remote atrophy after stroke.

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.

Neuropsychological profile of bilateral paramedian infarctions: three cases

INTRODUCTION

The thalamus is one of the strategic diencephalic structures of the human brain. The artery of Percheron, an asymmetrical common trunk arising from a P1 segment of the posterior cerebral artery, is a peculiar presentation of the three variants involved in the irrigation of the paramedian thalamic territory. Occlusion of this artery results in bilateral median thalamic infarction. The paramedian syndrome includes an acute loss or reduction of consciousness, often associated with oculomotor and neuropsychological disturbances.

PATIENTS AND METHODS

We present three cases of bilateral paramedian thalamic infarction with onset of acute coma, followed by fluctuations in the level of consciousness, memory, and behavioural alterations. A neuroradiological study with MRI identified individual thalamic nuclei, and a complete neuropsychological study was performed one month after onset of ictus.

RESULTS

One of the patients showed severe memory and executive function impairments without improvement of vertical gaze palsy. The other two patients presented with mild executive dysfunction with complete resolution of neurological symptoms. Neuroimaging results showed a bilateral lesion of the dorsomedial nuclei in the three patients.

CONCLUSIONS

Severe amnesia has been associated with an affection of the structures of the paramedian thalamic territory. Presently, the role of the dorsomedial nucleus remains controversial, with the suggestion that memory deficits observed in this type of lesion could be secondary to executive function deficits. In our case, the patient with the most severe dysexecutive deficit presented the most severe memory impairments.

Unraveling the contributions of the diencephalon to recognition memory: a review

Both clinical investigations and studies with animals reveal nuclei within the diencephalon that are vital for recognition memory (the judgment of prior occurrence). This review seeks to identify these nuclei and to consider why they might be important for recognition memory. Despite the lack of clinical cases with circumscribed pathology within the diencephalon and apparent species differences, convergent evidence from a variety of sources implicates a subgroup of medial diencephalic nuclei. It is supposed that the key functional interactions of this subgroup of diencephalic nuclei are with the medial temporal lobe, the prefrontal cortex, and with cingulate regions. In addition, some of the clinical evidence most readily supports dual-process models of recognition, which assume two independent cognitive processes (recollective-based and familiarity-based) that combine to direct recognition judgments. From this array of information a "multi-effect multi-nuclei" model is proposed, in which the mammillary bodies and the anterior thalamic nuclei are of preeminent importance for recollective-based recognition. The medial dorsal thalamic nucleus is thought to contribute to familiarity-based recognition, but this nucleus, along with various midline and intralaminar thalamic nuclei, is also assumed to have broader, indirect effects upon both recollective-based and familiarity-based recognition.

Differential impairment of remembering the past and imagining novel events after thalamic lesions

Vividly remembering the past and imagining the future (mental time travel) seem to rely on common neural substrates and mental time travel impairments in patients with brain lesions seem to encompass both temporal domains. However, because future thinking-or more generally imagining novel events-involves the recombination of stored elements into a new event, it requires additional resources that are not shared by episodic memory. We aimed to demonstrate this asymmetry in an event generation task administered to two patients with lesions in the medial dorsal thalamus. Because of the dense connection with pFC, this nucleus of the thalamus is implicated in executive aspects of memory (strategic retrieval), which are presumably more important for future thinking than for episodic memory. Compared with groups of healthy matched control participants, both patients could only produce novel events with extensive help of the experimenter (prompting) in the absence of episodic memory problems. Impairments were most pronounced for imagining personal fictitious and impersonal events. More precisely, the patients' descriptions of novel events lacked content and spatio-temporal relations. The observed impairment is unlikely to trace back to disturbances in self-projection, scene construction, or time concept and could be explained by a recombination deficit. Thus, although memory and the imagination of novel events are tightly linked, they also partly rely on different processes.

Vascular thalamic amnesia: a reappraisal

In humans lacunar infarcts in the mesial and anterior regions of the thalami are frequently associated with amnesic syndromes. In this review paper, we scrutinized 41 papers published between 1983 and 2009 that provided data on a total of 83 patients with the critical ischemic lesions (i.e. 17 patients with right-sided lesions, 25 with left-sided lesions and 41 with bilateral lesions). We aimed to find answers to the following questions concerning the vascular thalamic amnesia syndrome: (i) Which qualitative pattern of memory impairment (and associated cognitive and behavioral deficits) do these patients present? (ii) Which lesioned intrathalamic structures are primarily responsible for the amnesic syndrome? (iii) Are the recollection and familiarity components of declarative memory underlain by the same or by different thalamic structures? Results of the review indicate that, similar to patients with amnesic syndromes due to mesio-temporal lobe damage, patients with vascular thalamic amnesia display a prevalent deficit of declarative anterograde long-term memory, a less consistent deficit of declarative retrograde long-term memory and substantially spared short-term and implicit memory. Unlike mesio-temporal lobe patients, however, vascular thalamic amnesics often present dysexecutive and behavioral deficits similar to those observed in patients with frontal damage. The presence of an amnesic syndrome in patients with thalamic lacunar infarcts is strongly predicted by involvement of the mammillo-thalamic tract, which connects the anterior nuclei complex to the hippocampus proper via the fornix and the mammillary bodies. Finally, data reported in a few single cases provide support for the hypothesis that thalamic regions connected to distinct areas of the mesio-temporal lobe play differential roles in recollection and familiarity processes. The mammillo-thalamic tract/anterior nuclei axis seems primarily implicated in recollective processes, whereas the ventroamygdalofugal pathway/medio-dorsal axis primarily underlies familiarity processes.

Cognitive, affective and behavioural disturbances following vascular thalamic lesions: a review

During the last decades, many studies have shown that the thalamus is crucially involved in language and cognition. We critically reviewed a study corpus of 465 patients with vascular thalamic lesions published in the literature since 1980. 42 out of 465 (9%) cases with isolated thalamic lesions allowed further neurocognitive analysis. On the neurolinguistic level, fluent output (=31/33; 93.9%), normal to mild impairment of repetition (=33/35; 94.3%), mild dysarthria (=8/9; 88.9%) and normal to mild impairment of auditory comprehension (=27/34; 79.4%) were most commonly found in the group of patients with left and bilateral thalamic lesions. The taxonomic label of thalamic aphasia applied to the majority of the patients with left thalamic damage (=7/11; 63.6%) and to one patient with bithalamic lesions (=1/1). On the neuropsychological level, almost 90% of the left thalamic and bithalamic patient group presented with amnestic problems, executive dysfunctions and behaviour and/or mood alterations. In addition, two thirds (2/3) of the patients with bilateral thalamic damage presented with a typical cluster of neurocognitive disturbances consisting of constructional apraxia, anosognosia, desorientation, global intellectual dysfunctioning, amnesia, and executive dysfunctions associated with behaviour and/or mood alterations. Our study supports the long-standing view of a 'lateralised linguistic thalamus' but restates the issue of a 'lateralised cognitive thalamus'. In addition, critical analysis of the available literature supports the view that aphasia following left or bithalamic damage constitutes a prototypical linguistic syndrome.

Bilateral dorsolateral thalamic lesions disrupts conscious recollection

In an earlier study we disputed the claim that the mediodorsal thalamic nucleus is critical for familiarity. We reported patient (QX) who showed a severe deficit in conscious recollection, and behavioural problems (disinhibition, emotional lability) with relative sparing of familiarity-aware memory following a left mediodorsal thalamic lesion. More recent MR imaging has revealed that QX's lesions are more extensive than previously reported and involve both dorsolateral thalamic nuclei, and whilst there is evidence of left mediodorsal thalamic damage, it is not the main focus of damage. This paper reports a full analysis of QX's thalamic pathology alongside a more detailed investigation of his recognition memory, using yes/no and forced-choice procedures, and executive function. The results revealed impairments in yes/no recognition and conscious recollection rates of famous, artist and unknown names. In addition to the previously noted behavioural disinhibition and emotional lability, a deficit in spontaneous planning ability was evident on the Zoo Map Test (subtest of the Bahavioural Assessment of the Dysexecutive Syndrome). Forced-choice recognition, familiarity estimates and remote memory showed higher levels of preservation. The findings indicate that the dorsolateral thalamus is part of the extended hippocampal circuit which is causally critical only for recall and conscious recollection of complex associations rather than for the more automatic processes linked with novelty detection.

Mild topographical memory impairment following crossed unilateral lesions of the mediodorsal thalamic nucleus and the inferotemporal cortex

Monkeys with crossed unilateral lesions of the dorsomedial thalamus and contralateral ablations of the inferotemporal cortex were mildly impaired on acquisition and retention of visual conditional tasks requiring the integration of information about objects and their positions in space. They were not impaired on other conditional and nonconditional tasks. This impairment pattern resembles, qualitatively, that found following crossed unilateral lesions of the anterior thalamus and the inferotemporal cortex or bilateral lesions of the anterior and mediodorsal thalamic nuclei. Although the flow of visual information from the inferotemporal cortex through the hippocampal-fornix-anterior thalamic circuit plays a major part in memory for objects in places, the flow of information between inferotemporal cortex and mediodorsal thalamus, possibly by means of the frontal cortex, also makes some contribution.

Bilateral Thalamic Lesions Affect Recollection-and Familiarity-Based Recognition Memory Judgments

The contribution of the thalamus to different forms of explicit memory is poorly understood. In the current study, explicit memory performance was examined in a 40-year-old male (RG) with bilateral anterior and medial thalamic lesions. Standardized tests indicated that the patient exhibited more severe recall than recognition deficits and his performance was generally worse for verbal compared to nonverbal memory. Recognition memory tests using the remember-know (R/K) procedure and the confidence-based receiver operating characteristic (ROC) procedure were used to examine recollection- and familiarity-based recognition. These tests revealed that RG had deficits in recollection and smaller, but consistent deficits in familiarity. The results are in agreement with models indicating that the anteromedial thalamus is important for both recollection- and familiarity-based recognition memory.

Involvement of the mediodorsal thalamic nucleus in mediating recollection and familiarity

The mediodorsal (MD) thalamic nucleus is thought to play an important role in memory processes. Distinct hippocampal-thalamic-prefrontal connections have been described as the potential neural substrate for both, recollection and familiarity. The aim of this study was to investigate whether the MD is part of the circuits underlying these two memory components. We assessed the effects of ischemic thalamic lesions with or without MD involvement on performance in a word list discrimination task and standard tests of memory and executive function. Estimates of recollection and familiarity were derived using the dual-process signal-detection model (DPSD). The results revealed impairments in both, recollection and familiarity, after unilateral thalamic damage, with recollection being more affected than familiarity. There were no significant differences in the memory performance of patients with MD lesions compared to patients with ventrolateral-thalamic lesions except for familiarity estimates, which were lower for the latter group. Lesions involving the MD led to recollection deficits, although inspection of individual cases suggested a decrease in both memory components after damage in the medial part of this nucleus. Executive dysfunction was associated with lateral MD lesions and also ventrolateral-thalamic damage. The findings suggest that MD contributes to recollection, with some preliminary evidence of a contribution of the medial MD to familiarity. The small sample size does, however, not yet allow any clear conclusions in this regard. Since damage in the ventrolateral thalamus leads to memory and executive dysfunction, further research is needed to elucidate the role of this thalamic region in cognition.

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.

Learning impairments in monkeys with combined but not separate excitotoxic lesions of the anterior and mediodorsal thalamic nuclei

Clinical studies in humans and experiments in macaques suggest that damage to the anterior and the mediodorsal thalamus can induce a moderate amnesia, but a more dense impairment may result from substantial damage within the temporal lobes or their subcortical connections. Lesions of the anterior thalamus in macaques produce impairments which resemble those seen after lesions of the fornix-mamillary pathway, which carries projections from the hippocampus to the anterior thalamus, while lesions of the mediodorsal thalamus, which receives inputs from frontal and temporal cortex, produce moderate impairments on a wider range of memory tasks. In the present study, we have made bilateral excitotoxic lesions of either the anterior or the mediodorsal thalamus, or both, in marmoset monkeys. Monkeys with lesions of both thalamic nuclei were severely impaired on retention and new learning of examples of the visuospatial conditional task, a task which is specifically impaired by lesions of the fornix or hippocampus. They were not impaired on performance of a visuovisual conditional task on which monkeys with hippocampal lesions are impaired, nor were they impaired on any visual discrimination task, including the concurrent discrimination task on which monkeys with temporal neocortical ablations are impaired. Monkeys with separate lesions of either the anterior or the mediodorsal thalamus were not impaired on any of these tasks. These results suggest that the mediodorsal thalamus and the anterior thalamus are both involved in processing the output of the hippocampal-fornix-thalamic circuit. Dense amnesia may result from damage to circuits additional to the temporal lobe efferents to either the anterior or the mediodorsal nuclei.

Memory impairment and deep brain structures

Clinical and neuropsychological investigations were performed using the Luriya method in 141 patients with arteriovenous malformations (AVM). These included 27 patients with AVM in different parts of the caudate nucleus, 34 with AVM in the thalamus, 39 with AVM in the hippocampal formation, and 41 with AVM in the cingulate gyrus. A total of 102 patients underwent surgery. Patients with AVM in various locations showed common memory impairments as well as individual features of memory disturbances depending on which structures were affected. The common feature was the development of an amnesiac symptom complex resembling Korsakov's syndrome. These lesions developed only in patients with combined damage to deep structures (preoperatively in patients with ventricular hemorrhages); with the exception of patients with AVM of the caudate nucleus, memory impairments were modality-non-specific; all patients showed impairment of auditory-speech memory at the late phase and of visual memory in terms of indirect recall. Memory impairments characteristic of lesions to individual structures were the presence of functional asymmetry of memory defects in available of the caudate nucleus and thalamus (if only speech problems were present) and constant inclusions and contaminations in patients with AVM of the cingulate gyrus. It is suggested that certain aspects of memory function may have been duplicated in different structures during evolution and that each structure makes its own contribution to overall memory function.

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.

Thiamin deficiency and Korsakoff's syndrome: failure to find memory impairments following nonalcoholic Wernicke's encephalopathy

Prolonged alcohol consumption is associated with a variety of neuropsychiatric conditions, including the dense amnesic disorder known as Korsakoff's syndrome. Korsakoff's syndrome is frequently diagnosed in alcoholics after an episode of acute thiamin deficiency. The accepted view within the medical literature is that the etiology of this disorder lies in thiamin deficiency or Wernicke's encephalopathy. However, examination of the published reports of pure thiamin deficiency unaccompanied by chronic and excessive consumption of alcohol shows that, in this group of patients, the rate of progression to Korsakoff's syndrome is low. This result suggests that the memory impairments associated with alcohol-related brain damage cannot be attributed to thiamin deficiency alone. The etiology of alcohol-related cognitive impairments such as Korsakoff's syndrome is still poorly understood but several lines of evidence suggest multiple causal factors interact to produce deficits in performance. Animal models that manipulate only a single putative etiological factor are unlikely to elucidate the multiple influences that lead to Korsakoff's syndrome. A study of the natural history of alcohol-related brain damage is needed that will allow an assessment of individual risk factors and their interactions.

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.

Modification of neuromagnetic cortical signals by thalamic infarctions

Auditory evoked responses and spontaneous cortical activity were recorded with a whole-scalp 122-channel neuromagnetometer from 7 patients, who had small thalamic infarctions in the region of the left anterior tuberothalamic artery and associated memory defects. In contrast to healthy control subjects, with dominant rhythmic activity at 10.6 +/- 0.6 Hz in the parieto-occipital region, the spectral maximum in the patients was at 8.9 +/- 0.4 Hz. Abnormal acceleration of rhythmic activity was also observed bilaterally in rolandic areas. Our findings imply that lesions of non-specific thalamic nuclei may disturb human brain rhythms in widespread cortical areas. 'Mismatch responses' to deviant tones (1.1 kHz) among standards (1.0 kHz), suggested to reflect sensory auditory memory in healthy subjects, were absent in 2 patients, markedly decreased in 3, and normal in 2, implying that pathways passing through the anteromedial thalamus contribute to modulation of these responses. We conclude that local unilateral lesions in the anteromedial thalamus may cause extensive, bilateral alterations in the brain's electric activity.

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 anatomy of long-term memory

Memory in the brain is organized into multiple memory systems that perform different memory functions and have different neurologic substrates. Declarative memory involves conscious memory for facts and events. The medial temporal lobe and structures in the diencephalon are essential in the establishment of new declarative memories, and these memory traces are finally stored in domain-specific regions of the cerebral cortex. The frontal lobe and basal ganglia are important in some forms of declarative memory that require reasoning about the contents of memory. Nondeclarative forms of memory (including skill learning, repetition priming, and classical conditioning) do not involve conscious recollection and are measured through changes in the way in which tasks are performed. These forms of memory rely upon the cerebral cortex, basal ganglia, and cerebellum.

Thalamic amnesia following venous infarction: evidence from a single case study

The present paper describes the case of a right-handed Italian-English bilingual male patient suffering from amnesia following a bilateral thalamic lesion due to venous infarction. Within a few months from the onset, the lesion gradually shrank and was finally confined to the left thalamus only, in particular to the antero-medial portion and the pulvinar. The mammillary bodies and the cortical areas of both hemispheres were spared. After the regression of a series of generalized cognitive deficits implying slow psychic activity confusion, and spatial and temporal disorientation, the patient presented a persistent amnesic syndrome with mild language disorders, both in Italian and in English. Major disorders of memory included a dissociation between verbal memory, which was severely impaired, and spatial memory, which was largely preserved.

Diencephalic temporal order amnesia

OBJECTIVE

Amnesia for temporal relations may occur without amnesia for content memories. The aim was to determine whether a patient with mild memory loss due to a thalamic lesion had amnesia for temporal relations, and whether the amnesia was specific for particular material.

METHODS

A male patient had an isolated right dorsomedial thalamic infarct and resolving amnesia. He was tested on tasks relating to content (what) and temporal (when) memories for both verbal and non-verbal material, three and seven months after his infarct.

RESULTS

Three months after his infarct, the man had amnesia for temporal, but not content memories using non-verbal stimuli, and normal performance using verbal stimuli. Seven months after his infarct, he had a normal performance using verbal and non-verbal stimuli.

CONCLUSIONS

Patients with thalamic lesions may have a material specific amnesia for temporal relations in the absence of amnesia for content.

The relationships between temporal lobe and diencephalic structures implicated in anterograde amnesia

The relationship between the anterograde amnesic syndromes associated with diencephalic and temporal lobe pathology is examined in the light of recent findings. It is proposed that a common feature of anterograde amnesia is damage to part of an "extended hippocampal system" comprising the hippocampus, the fornix, the mammillary bodies, and the anterior thalamic nuclei. Damage to this system results in deficits in the recall of episodic information, the core symptom of anterograde amnesia. In contrast, lesions in this system need not disrupt tests of recognition memory when they primarily tax familiarity judgements. It is assumed that familiarity judgements depend on other regions (e.g. the rhinal cortex in the case of temporal lobe amnesia) and that the extended hippocampal system is principally involved in those aspects of recognition that are retrieval-based rather than familiarity-based. These proposals arise from new evidence on the performance of delayed nonmatching-to-sample by animals, from a meta-analysis of the performance of amnesic subjects on a test of recognition memory, and from new research into the pattern of connections between the medial temporal lobe and the medial diencephalon in primates.

Anterograde but not retrograde memory loss following combined mammillary body and medial thalamic lesions

We report the first human case of combined mammillary body and medial thalamic lesions due to focal pathology. A patient presented with a multi-lobular lesion that affected the mammillary bodies, the medial thalamus and the brain stem. On neuropsychological testing, he showed significant anterograde memory impairment, with marked impairment on delayed story recall, but normal or only mildly impaired performance on retrograde memory tasks. Our findings corroborate the results of recent non-human lesion studies and indicate that some of the well-established features of the amnesic syndrome, such as severe retrograde amnesia, may not be due to primary diencephalic pathology. Significant retrograde amnesia may result from cortical pathology or from an interaction between cortical and subcortical pathology.

Transient global amnesia and cerebral infarct: a case report

Transient global amnesia refers to a sudden and isolated dysfunction of memory for recent events, lasting a few hours. The pathogenesis of this neurological disorder is still uncertain. The most accepted hypotheses concern ischaemic, epileptic and migraine causes. We now report a case of transient global amnesia associated with computed tomography evidence for a hypodense area in the left thalamus 10 days after the transient memory dysfunctions.

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.

Dissociation of declarative and nondeclarative memory after bilateral thalamic lesions: a case report

The case of a 63-year-old woman who suffered bilateral ischemic damage in the region of blood supply of the paramedian thalamic arteries is reported. She displayed severe deficits on immediate and delayed recall of both verbal and visuospatial material in the presence of intact IQ and attentional abilities. Performance on tests of all major components of nondeclarative memory (skill acquisition, perceptual priming, classical conditioning) was also preserved. The present report, thus, provides a further example for dissociations of declarative and nondeclarative memory functions following bilateral thalamic damage.

Medial thalamotomy with the Leksell Gamma Knife for treatment of chronic pain

The authors describe 10 patients who underwent stereotactic medial thalamotomy with the Leksell Gamma Knife for treatment of chronic intractable pain. The pain was related to structural spinal disorders (4), postherpetic neuralgia (2), spinal cord injury (1), thalamic syndrome (1), anesthesia dolorosa of the face (1), and brainstem infarction (1). All patients had undergone extensive treatment with a variety of modalities prior to gamma thalamotomy. Nine patients underwent unilateral and one patient bilateral lesions. Magnetic resonance imaging (MRI) was used for target localization and the lesions were directed toward the intralaminar nuclei, the lateral portion of the medial dorsal nucleus, the centrum medianum and parafascicular nuclei. The lesions were made with radiation doses of 160-180 Gy using a 4 mm beam collimator and either a single isocenter (1 patient) or two isocenters (9 patients). Follow-up MRI scans in all patients showed well localized lesions. Three patients experienced excellent pain relief, four had good pain relief and three were failures. No complications were seen in any of the patients. In the past gamma thalamotomy was used mainly for treatment of pain related to malignancies but our results indicate that it may also be a safe and effective treatment for pain of nonmalignant origin as well.

Convex third ventricle: a possible sign for dementia using MRI

The shape and thickness of the third ventricles were studied with magnetic resonance imaging in 46 patients under evaluation for memory impairment. We compared this population with 23 subjects imaged for other reasons. The study group consisted of patients with diagnoses of probable dementia of the Alzheimer's type (DAT; 35.6%), multi-infarct dementia (MID; 22.2%), depression (8.9%), alcoholic dementia (6.7%), other dementias (OD; 13.2%) and no dementia (6.7%). Within the study group, there were no significant differences across diagnostic categories for duration of symptoms or level of education. Patients with DAT were, however, more impaired than others (Mini-Mental State Examination scores: DAT 14.6 [+/- 8.2] versus MID 17.4 [+/- 6.2] versus OD 21.2 [+/- 6.4]). Demented subjects were more likely than nondemented individuals to have a convex third ventricle and greater wall separation. The results suggest that the shape of the third ventricle may correlate with dementia. Possibly, the dorsal medial nucleus of the thalamus is involved in the dementia.

Dysarthria in bilateral thalamic infarction. A case study

A patient suffering from bilateral thalamic infarction in the region supplied by the paramedian arteries sparing the internal capsules underwent acoustic analysis of sentence utterances. The results were compared with the findings obtained in parkinsonian subjects, in patients with upper motor neuron lesions, and in normal subjects. Acoustic measurements revealed increased pitch, monotonous speech, rough voice quality, and normal speech tempo concomitant with articulatory impreciseness in terms of incomplete closure productions. This constellation resembled parkinsonian dysarthria. Damage to the thalamic projection area of the pallidal efferents, therefore, seems to be the most probable cause of the patient's speech disorders. In parkinsonian subjects stereotactical lesions of this structure ameliorate rigor, but not akinesia. Thus, our patient's speech deficits, and by analogy the corresponding parkinsonian dysarthric disturbances, may be considered akinetic signs.

Paramedian thalamopeduncular infarction: clinical syndromes and magnetic resonance imaging

We prospectively examined 11 patients with magnetic resonance imaging-documented infarction in the paramedian thalamopeduncular region, which is supplied by the superior mesencephalic and posterior thalamosubthalamic arteries. Variations in the size and rostral-caudal extent of infarction correlated with the following three clinical patterns: (1) With unilateral paramedian mesencephalic infarction, an ipsilateral third nerve paresis was accompanied by mild contralateral hemiparesis or hemiataxia. Contralateral ptosis and impaired upgaze were observed in two patients; one of them showed additional damage to the posterior commissure. (2) With bilateral infarction in the thalamopeduncular junction, involving the mesencephalic reticular formation, supranuclear vertical gaze defects were accompanied by impaired consciousness or memory, and mild aphasia in some patients. Persistent amnesia was observed only when the dominant anterior nucleus or mamillothalamic tract was damaged. (3) With larger thalamopeduncular infarcts, partial or complete third nerve paresis was combined with supranuclear gaze disturbance and delayed contralateral tremor. An unusual gaze disorder, a variant of the vertical "one-and-a-half syndrome," occurred with a small strategically placed lesion at the thalamopeduncular junction, best explained by selective damage to supranuclear pathways or partial nuclear involvement. The primary cause of these infarctions was embolism to the basilar apex or local atheroma at the origin of the posterior cerebral artery.

Thalamic amnesia: Korsakoff syndrome due to left thalamic infarction

In order to support the concept that a lesion of the thalamus is sufficient to cause a Korsakoff syndrome, we are presenting 5 patients, all of whom developed the syndrome after sustaining a left (dominant) thalamic infarction. Two patients had pure thalamic strokes followed by a permanent Korsakoff syndrome. One of these patients was studied with neuropsychometric testing, as well as with a modern MRI scan. In 2 other patients, clinical and imaging data indicate that infarction was not limited to the thalamus. Another patient had bilateral thalamic infarcts but only a temporary Korsakoff syndrome. Neuropathological data are needed to elucidate the exact anatomical substrate of dominant thalamic Korsakoff syndrome.

"Fatal familial insomnia": neuropsychological study of a disease with thalamic degeneration

Fatal Familial Insomnia (FFI) is an inherited disease characterized clinically by sleep, autonomic and motor disturbances and pathologically by marked atrophy of the anterior and dorsomedial nuclei of the thalamus. The neuropsychological study of three cases of FFI showed: (1) a progressive disturbance of attention and vigilance, (2) a memory deficit with lability of mnesic traces and difficulty in manipulation and ordering of events, suggesting an alteration of working memory and (3) a deficit of frontal abilities with impairment in planning and prevision of events but preservation of general intelligence.

Vascular dementia: neuropathologic alterations and metabolic brain changes

After reviewing the concepts of dementia, in general, and vascular dementia, in particular, this review discusses potential future approaches that may contribute to an improved definition of the clinical syndrome and the neuropathological features of vascular dementia. Specific brain alterations in high-energy phosphate compounds, as measured by nuclear magnetic resonance, may contribute to the separation between dementias with neurodegenerative diseases and those with ischemic (vascular or hemodynamic) disorders.

An analysis of the correlation of lesion size, localization and behavioral effects in 283 published studies of cortical and subcortical lesions in old-world monkeys

The present article evaluates the quality and magnitude of the effects of lesion size and location and their interaction, on the behavioral performance of old world monkeys by a quantitative comparison of 283 published studies. The results indicate that lesion size alone is a poor predictor of the behavioral performance of monkeys, as opposed to Lashley's work in rats. Lesion location is a reliable predictor of the behavioral performance for brain regions thought to be primarily involved in a specific behavior; however, similar behavioral effects, although less reliable, can be observed for many different lesion loci, suggesting a specialized and a holistic brain functioning to be working at the same time. Some lesion loci are, in sharp contrast to current hypotheses about functional localization in the brain, not associated with impairments, but with significant improvements of a specific behavior. For such lesion loci the correlation of lesion size and behavioral performance may yield significant positive relationships (that is, increasing behavioral improvement with increasing lesion size); these relationships are contrasted by the significant negative relationships obtained for lesions of brain regions thought to be primarily involved in a given behavior. Thus, the lesion size may be a good predictor of the behavioral performance, depending on the lesion location and on the behavior under measurement. The behaviors analysed in this study were discrimination or delayed reaction or delayed matching-to-sample. The former two behaviors involve habit-like learning and are thought to be mediated by corticostriate functional pathways in the brain and the latter behavior implies the learning of single events, being thought to be mediated by corticolimbic functional pathways in the brain. Improved performances were observed for habit-like behaviors after lesions of brain regions (lateral frontal, premotor/motor, parietal, inferotemporal cortex, amygdala and fornix) being not primarily involved in a given behavior but possibly being able to inhibit the corticostriate pathways. Interestingly, lesions of subareas of the neostriatum were found to cause impairments in habit-like behaviors presumably being processed via these subareas (e.g. head of the caudate nucleus and delayed reaction), but to cause significant improvements in other behaviors (e.g. head of the caudate nucleus and visual discrimination). Thus, it may be concluded that diverse systems of functionally interconnected brain regions may maintain reciprocal inhibitions, with the result that a lesion within one system not only leads to a loss of one behavior, but in addition leads to a modification, may be a facilitation, of another behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of Metabolic Activity in the Diencephalon of Monkeys Performing Working Memory Task: A 2-Deoxyglucose Study in Behaving Rhesus Monkeys

The 2-deoxyglucose (2-DG) method was used to study the effect of working memory processing on local cerebral glucose utilization (LCGU) in the diencephalon of the rhesus monkey. Monkeys were given [14C]2-DG while performing either one of three tasks that engaged working memory (WORK group) or one of two control tasks (CONT group) that used associative or non associative processes. The tasks of the WORK group—spatial delayed response, spatial delayed alternation, and delayed object alternation—are alike in that the information guiding a correct response changes from trial to trial and only the accurate record of the preceding response (or cue) is relevant for each successive trial. The CONT group, in contrast, performed on either a visual pattern discrimination test, in which the correct stimulus–response association was invariant across all trials and all test sessions, or on a sensorimotor task in which there was no explicit memory requirement.

LCGU was examined in five diencephalic regions: the mammillary bodies, the anteroventral and anteromedial thalamus, and the parvocellular and magnocellular components of the mediodorsal thalamic nucleus. Comparisons across the two groups showed that mean LCGU in the anterior and mediodorsal thalamic nuclei was significantly elevated (by 12–16%) in the WORK group relative to the CONT group. Mean LCGU in the mammillary bodies also was higher in the WORK group than in the CONT group, but this difference was not significant.

The present findings suggest that the anterior and mediodorsal thalamic nuclei represent diecephalic components of a neural network processing working memory. Together with our previous report on the enhancement of metabolic activity in the hippocampus and dentate gyrus, these results show that working memory has a wide-ranging influence on cerebral metabolism and emphasize the cooperative, rather than dissociable, roles of the hippocampus and medial thalamus in this function.

Description of brain injury in the amnesic patient N.A. based on magnetic resonance imaging

N.A. has been amnesic since 1960 when at the age of 22 years he sustained a penetrating brain injury with a miniature fencing foil. The amnesia primarily affects verbal material and occurs in the absence of other detectable cognitive deficits. Previous CT scans demonstrated a lucency in the region of the left mediodorsal thalamic nucleus, but no additional damage was revealed. Beginning in 1986 when he was 48 years old, N.A. was evaluated with a series of magnetic resonance imaging (MR) studies. Three major areas of damage were identified. In the left thalamus there is a prominent 3- to 4-mm-wide linear lesion that approximates the position and orientation of the internal medullary lamina. The defect extends for approximately 20 mm anteroposteriorly and likely involves the rostral group of intralaminar nuclei (central medial, paracentral, central lateral, rhomboid, and reuniens nuclei), the caudal group of intralaminar nuclei (centrum medianum and parafascicular nuclei), the ventral aspect of the mediodorsal nucleus, and the ventral lateral and ventral anterior nuclei. It also likely interrupts the trajectories of the mammillothalamic tract and postcommissural fornix. The posterior hypothalamus is markedly disrupted and the mammillary nuclei appear to be missing bilaterally. Finally, the right anterior temporal lobe is damaged for a distance of about 3.5 cm from the pole to midway through the amygdaloid complex. This damage probably occurred during exploratory neurosurgery done at the time of N.A.'s injury. The hippocampal formation appears intact on both sides. A comparison of these findings with those from other patients with diencephalic amnesia suggests that amnesia can result when several diencephalic structures are damaged conjointly, including the internal medullary lamina, the intralaminar nuclei, the mediodorsal nucleus, and the mammillothalamic tract. Whether amnesia as severe as N.A.'s would result from selective damage to any one of these structures remains to be determined.

Diencephalic amnesia: a reorientation towards tracts?

The principal thalamic and hypothalamic structures implicated in mnemonic information processing are the mediodorsal nucleus of the thalamus, the pulvinar, anterior thalamus, and laterodorsal nucleus, the mamillary body, and the mamillothalamic tract and internal medullary lamina. Determining the contribution of an individual region in memory is quite difficult as it is nearly impossible to find a circumscribed damage of only one region. On the contrary, some illnesses affecting primarily the diencephalon, such as Korsakoff's disease, tend to involve several structures together. Furthermore, even when cases with similar circumscribed diencephalic damage can be found, these will not necessarily demonstrate the same outcome on the behavioral level. Therefore, the role or contribution of individual memory-related diencephalic structures has to be inferred by comparing a number of cases and by then extracting distinct features common to a given group. Such an approach revealed that the contributions of the two fiber systems mentioned above, mamillothalamic tract and internal medullary lamina, might be more important in processing information long-term than had been acknowledged previously and might be more important than that of the nuclear masses mentioned, especially of the mediodorsal thalamus. This outcome underlines the view that emphasizing interactions between brain regions rather than single static masses will provide a more realistic picture of how the nervous system acts in information processing.