Longitudinal assessment of chemotherapy-induced structural changes in cerebral white matter and its correlation with impaired cognitive functioning

PURPOSE

To uncover the neural substrate of cognitive impairment related to adjuvant chemotherapy, we studied cerebral white matter (WM) integrity before and after chemotherapy by using magnetic resonance diffusion tensor imaging (DTI) in combination with detailed cognitive assessment.

PATIENTS AND METHODS

Thirty-four young premenopausal women with early-stage breast cancer who were exposed to chemotherapy underwent neuropsychologic testing and DTI before the start of chemotherapy (t1) and 3 to 4 months after treatment (t2). Sixteen patients not exposed to chemotherapy and 19 age-matched healthy controls underwent the same assessment at matched intervals. In all groups, we used paired t tests to study changes in neuropsychologic test scores and whole-brain voxel-based paired t tests to study changes in WM fractional anisotropy (FA; a DTI measure that reflects WM tissue organization), with depression scores and intelligence quotient as included covariates. We correlated changes of neuropsychologic test scores with the mean change of FA for regions that survived the paired t tests in patients treated with chemotherapy.

RESULTS

In contrast to controls, the chemotherapy-treated group performed significantly worse on attention tests, psychomotor speed, and memory at t2 compared with t1 (P < .05). In the chemotherapy-treated group, we found significant decreases of FA in frontal, parietal, and occipital WM tracts after treatment (familywise error P < .05), whereas for both control groups, FA values were the same between t1 and t2. Furthermore, performance changes in attention and verbal memory correlated with mean regional FA changes in chemotherapy-treated patients (P < .05).

CONCLUSION

We report evidence of longitudinal changes in cognitive functioning and cerebral WM integrity after chemotherapy as well as an association between both.

Measuring extrastriatal dopamine release during a reward learning task

OBJECTIVES

Reward learning is critical for survival. Animal research emphasizes the role of dopaminergic (DA) mesocorticolimbic pathways in reward learning, but few studies have evaluated extrastriatal DA functioning in humans. The purpose of this study was to examine presynaptic DA release in extrastriatal regions of the reward circuit by measuring displacement of the high affinity D(2) /D(3) radioligand [(18) F]Fallypride during a reward task.

DESIGN

Ten healthy volunteers underwent a [(18) F]Fallypride positron emission tomography protocol while performing a reward task, allowing us to assess participants' ability to modulate behavior as a function of reward. DA receptor ligand displacement was correlated with task performance and self-reported anhedonia.

OBSERVATIONS

Parametric t-maps revealed significant decrease in [(18) F]Fallypride binding in the medial orbitofrontal cortex (mOFC), ventromedial prefrontal cortex (vmPFC), and dorsal anterior cingulate cortex (dACC), indicating endogenous DA release in these regions. Increasing anhedonic symptoms correlated with DA release in the left vmPFC, left dACC, and right dACC emerged (all r's > 0.65, P's < 0.05). Similarly, reduced reward learning correlated with higher DA release in left vmPFC, right vmPFC, and left dACC (all r's < -0.64, P's < 0.05). Left dACC (r = 0.66, P = 0.04) and left vmPFC (r = 0.74, P = 0.01) DA release showed a significant positive correlation with impaired tendency to modulate behavior as a function of prior positive reinforcements.

CONCLUSIONS

These findings support the hypothesis that DA release in mOFC, vmPFC, and dACC regions plays an important role in reinforcement learning in the human brain.

Chemotherapy-induced structural changes in cerebral white matter and its correlation with impaired cognitive functioning in breast cancer patients

A subgroup of patients with breast cancer suffers from mild cognitive impairment after chemotherapy. To uncover the neural substrate of these mental complaints, we examined cerebral white matter (WM) integrity after chemotherapy using magnetic resonance diffusion tensor imaging (DTI) in combination with detailed cognitive assessment. Postchemotherapy breast cancer patients (n = 17) and matched healthy controls (n = 18) were recruited for DTI and neuropsychological testing, including the self-report cognitive failure questionnaire (CFQ). Differences in DTI WM integrity parameters [fractional anisotropy (FA) and mean diffusivity (MD)] between patients and healthy controls were assessed using a voxel-based two-sample-t-test. In comparison with healthy controls, the patient group demonstrated decreased FA in frontal and temporal WM tracts and increased MD in frontal WM. These differences were also confirmed when comparing this patient group with an additional control group of nonchemotherapy-treated breast cancer patients (n = 10). To address the heterogeneity observed in cognitive function after chemotherapy, we performed a voxel-based correlation analysis between FA values and individual neuropsychological test scores. Significant correlations of FA with neuropsychological tests covering the domain of attention and processing/psychomotor speed were found in temporal and parietal WM tracts. Furthermore, CFQ scores correlated negatively in frontal and parietal WM. These studies show that chemotherapy seems to affect WM integrity and that parameters derived from DTI have the required sensitivity to quantify neural changes related to chemotherapy-induced mild cognitive impairment.

[Imaging of language and communication in dementia]

BACKGROUND

Social interaction in patients with dementia is compromised by language problems and impairment of other cognitive domains involved in communication.

AIM

To describe language and communication problems in patients with dementia and to provide insight into the neurological basis of these problems.

METHOD

Our study is based on some of our own research findings and on relevant literature concerning the imaging of language and communication in patients with Alzheimer's disease and frontotemporal degeneration.

RESULTS

Imaging revealed that the clinical expression of communicative disorders in patients with cortical neurodegeneration depends on regional brain atrophy and a possible functional reorganisation triggered by neuropathological changes.

CONCLUSION

Brain imaging increases our knowledge about the pathogenesis of communicative disorders in dementia.

Gesture discrimination in primary progressive aphasia: the intersection between gesture and language processing pathways

The issue of the relationship between language and gesture processing and the partial overlap of their neural representations is of fundamental importance to neurology, psychology, and social sciences. Patients suffering from primary progressive aphasia, a clinical syndrome characterized by comparatively isolated language deficits, may provide direct evidence for anatomical and functional association between specific language deficits and gesture discrimination deficits. A consecutive series of 16 patients with primary progressive aphasia and 16 matched control subjects participated. Our nonverbal gesture discrimination task consisted of 19 trials. In each trial, participants observed three video clips showing the same gesture performed correctly in one clip and incorrectly in the other two. Subjects had to indicate which of the three versions was correct. Language and gesture production were evaluated by means of conventional tasks. All participants underwent high-resolution structural and diffusion tensor magnetic resonance imaging. Ten of the primary progressive aphasia patients showed a significant deficit on the nonverbal gesture discrimination task. A factor analysis revealed that this deficit clustered with gesture imitation, word and pseudoword repetition, and writing-to-dictation. Individual scores on this cluster correlated with volume in the left anterior inferior parietal cortex extending into the posterior superior temporal gyrus. Probabilistic tractography indicated this region comprised the cortical relay station of the indirect pathway connecting the inferior frontal gyrus and the superior temporal cortex. Thus, the left perisylvian temporoparietal area may underpin verbal imitative behavior, gesture imitation, and gesture discrimination indicative of a partly shared neural substrate for language and gesture resonance.

Fear conditioning following a unilateral anterior temporal lobectomy: reduced autonomic responding and stimulus contingency knowledge

Animal research demonstrated that during fear conditioning the amygdala plays a central role in forming an association between the conditioned stimulus (CS) and the unconditioned stimulus (US). Lesion studies conducted in patients who underwent a unilateral anterior temporal lobe resection, however; yielded contradictory findings. To date, it remains unclear whether amygdala damage only affects fear-conditioned startle responding or impairs both the latter and fear-conditioned skin conductance responding (SCR). Moreover inconsistency exists regarding the preservation of contingency knowledge in amygdala-damaged patients. In the current study, a differential fear conditioning task was presented to a unilaterally amygdala-damaged patient group and a healthy control group, recording fear-potentiated startle responses along with SCRs. Retrospectively, the valence of the CSs and contingency awareness was assessed. Unlike the control group, unilaterally amygdala-damaged patients showed neither in their SCRs nor in their valence ratings an effect of fear conditioning. The startle data, however, yielded in none of the two test groups fear-conditioned responding. Finally, considerably fewer patients (37.5%) than controls (95%) acquired correct memory of the presented contingency. Based on these findings we concluded that the fear conditioning impairment in amygdala-damaged patients was not restricted to SCRs, but also affected valence ratings and memory of the presented contingency. A broader theory of the amygdala as relevance detector is proposed in order to account for the diverse neurological findings obtained so far.

Classically conditioned fear responses are preserved following unilateral temporal lobectomy in humans when concurrent US-expectancy ratings are used

Previous lesion studies demonstrate that patients who underwent a unilateral temporal lobe resection show impaired skin conductance responding (SCR) to aversively conditioned stimuli. The aim of the current lesion study was to examine whether the amygdala is also critically involved in differential SCR during a more explicit form of fear learning. A simple discrimination task was presented to a unilaterally amygdala-damaged patient group and a control group, in which one neutral stimulus was always followed by an electric shock (CS+), whereas a second stimulus always appeared alone (CS-). To direct attention towards the stimulus contingencies, participants were asked to predict the occurrence of the shock continuously throughout the whole task. The results revealed that patients and controls rapidly acquired contingency knowledge as measured by the online US-expectancy ratings. Crucially, both test groups showed differential SCRs during CS+ and CS- trials. Thus, contrary to earlier findings, robust conditioned SCRs can be obtained in patients with unilateral temporal lobe resection as long as they are able to acquire explicit stimulus contingency knowledge. The two-level account of Ohman and Mineka [Ohman, A., & Mineka, S. (2001). Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychological Review, 108, 483-522] is proposed in order to explain the diverse lesion data obtained so far.

Whole-body biodistribution and radiation dosimetry of 18F-GE067: a radioligand for in vivo brain amyloid imaging

We have characterized the biodistribution and dosimetry of (18)F-3'-F-6-OH-BTA1 ((18)F-GE067), a newly developed radioligand to visualize and quantify amyloid burden, in healthy elderly human subjects.

METHODS

Six subjects (5 men and 1 woman; age range, 51-74 y) underwent dynamic whole-body PET/CT for 6 h after a bolus injection of (18)F-GE067. Source organs were delineated on PET/CT. Individual organ doses and effective doses were determined.

RESULTS

No adverse events or clinically significant changes were observed. (18)F-GE067 is excreted predominantly through the hepatobiliary system. The gallbladder, upper large intestine, and small intestine are the organs with the highest absorbed dose (average, 287, 173, and 155 microGy/MBq, respectively). The mean effective dose was 33.8 +/- 3.4 microSv/MBq, a dose comparable to that of many other (18)F-labeled radiopharmaceuticals.

CONCLUSION

The estimated effective dose of (18)F-GE067 for PET amyloid imaging was acceptable (class II-b defined by the World Health Organization), and relatively low variability between subjects was observed.

Relationship of type 1 cannabinoid receptor availability in the human brain to novelty-seeking temperament

CONTEXT

Brain neurochemistry can partially account for personality traits as a variance of normal human behavior, as has been demonstrated for monoamine neurotransmission. Positron emission tomography using fluorine 18-labeled MK-9470 now enables quantification of type 1 cannabinoid receptors (CB1R) in the brain.

OBJECTIVE

To investigate whether there is a relationship between human temperament traits and regional cerebral CB1R availability.

DESIGN

Forty-seven [(18)F]MK-9470 baseline scanning sessions were performed and correlated with the temperament dimensions and subdimensions of the 240-item Cloninger Temperament and Character Inventory.

SETTING

Academic brain imaging center.

PARTICIPANTS

Forty-seven nonsmoking, healthy volunteers (paid). Main Outcome Measure Voxel-based correlation of temperament variables of the inventory with regional CB1R availability.

RESULTS

Novelty seeking was inversely correlated with global CB1R availability (r = -0.33, P = .02), with the most significant correlation in the left amygdala (r = -0.41, P = .005). In particular, the subdimension extravagance showed a highly significant inverse correlation to global CB1R availability (r = -0.53, P <.001), most pronounced in the amygdala, anterior cingulate, parietal cortex, and precuneus. Also, disorderliness was inversely correlated with global CB1R availability (r = -0.31, P = .04).

CONCLUSIONS

Low baseline cerebral CB1R availability is related to a high novelty-seeking personality, in particular to extravagance, most pronounced in the amygdala. Further investigation of the functional role of the CB1R is warranted in pathological behavior known to be strongly related to novelty seeking, such as addiction and eating disorders.

Abeta amyloid deposition in the language system and how the brain responds

Post-mortem measures of Abeta amyloid deposition correlate only weakly with cognitive dysfunction antemortem. We tested the hypothesis that functional reorganization forms a critical intermediary step between Abeta amyloid-associated brain injury and clinical disease expression. Fifteen patients with early-stage probable Alzheimer's disease (AD) and 16 cognitively intact controls participated in this combined functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) study. The fMRI design had two factors: task (associative-semantic versus visuoperceptual judgement) and input-modality (written words versus pictures). We measured Abeta amyloid by means of Pittsburgh Compound B (11C-PIB). In the posterior third of the left superior temporal sulcus (STS), the fMRI response during the associative-semantic compared with the visuoperceptual task was lower in AD than in controls, in particular for words. Response amplitude correlated inversely with PIB uptake in this region. Contralaterally, the functional pattern differed substantially: the fMRI response in the right posterior STS during the associative-semantic versus the visuoperceptual task was higher in AD than in controls. Accuracy on the Boston Naming test correlated positively with the degree to which AD patients were able to recruit the right STS (r = 0.84, P(corrected) = 0.014). PIB uptake did not correlate with naming accuracy. Functional reorganization of the language system in response to Abeta amyloid-related brain injury exists in early-stage AD and determines the degree of anomia more than Abeta amyloid load per se does.

Automatic affective stimulus processing is intact after unilateral resection of the anterior temporal lobe in humans

Only hundreds of milliseconds after an incoming stimulus is perceived, we make an evaluation of whether it is good or bad. This evaluation seems to occur automatically and can significantly influence behavior. According to several functional imaging studies, the amygdala, which is localized in the temporal lobes of the brain, is an important structure for the automatic processing of affective stimuli. To investigate how critical a role the amygdala plays in this process, we had 20 participants with unilateral resection of the temporal lobe and 20 controls perform an affective priming task. Both controls and patients demonstrated shorter response latencies on trials where prime and target had the same valence than on trials where prime and target had the opposite valence. This finding is generally known as the affective priming effect and is considered to reflect automatic stimulus evaluation. More specifically, it is assumed that the valence of the prime stimulus is activated automatically and exerts an influence on the speed by which the target stimulus is evaluated. Given that the affective priming effect is equally large in both groups, our results suggest that the automatic processing of stimulus valence is intact in participants who sustained unilateral resection of the temporal lobe.

Alzheimer dementia caused by a novel mutation located in the APP C-terminal intracytosolic fragment

Since the first report showing that Alzheimer disease (AD) might be caused by mutations in the amyloid precursor protein gene (APP), 20 different missense mutations have been reported. The majority of early-onset AD mutations alter processing of APP increasing relative levels of Abeta42 peptide, either by increasing Abeta42 or decreasing Abeta40 peptide levels or both. In a diagnostic setting using direct sequence analysis, we identified in one patient with familial early-onset AD a novel mutation in APP (c.2172G>C), predicting a K724N substitution in the intracytosolic fragment. The mutation is located downstream of the epsilon-cleavage site of APP and is the furthermost C-terminal mutation reported to date. In vitro expression of APP K724N cDNA showed an increase in Abeta42 and a decrease in Abeta40 levels resulting in a near three-fold increase of the Abeta42/Abeta40 ratio. Further, in vivo amyloid positron emission tomography (PET) imaging revealed significantly increased cortical amyloid deposits, supporting that in human this novel APP mutation is likely causing disease.

Knowledge of visual attributes in the right hemisphere

Neurobiological theories of knowledge processing are biased toward the language-dominant (usually the left) hemisphere. Does the right hemisphere critically contribute to knowledge processing? J.A. is a left-hemisphere language-dominant individual who suffered a lesion confined to the right mid- and anterior fusiform gyrus. Although her language abilities are intact, she showed a partial loss of knowledge of the visual attributes of biological and nonbiological entities. This was observed regardless of the task performed: object discrimination, oral feature generation, forced-choice naming-to-definition or free-hand drawing. Functional-associative and nonvisual sensory attributes were spared. The same region that was lesioned in J.A. was activated in a functional magnetic resonance imaging study in 27 volunteers who retrieved semantic associations between concepts, but only if the concepts were represented as pictures and not as words. Therefore, right fusiform gyrus critically contributes to the conscious recollection of visual attributes of familiar entities.

Word Reading and Posterior Temporal Dysfunction in Amnestic Mild Cognitive Impairment

Patient studies that combine functional magnetic resonance imaging with chronometric analysis of language dysfunction may reveal the critical contribution of brain areas to language processes as well as shed light on disease pathogenesis. In amnestic mild cognitive impairment (MCI), a prodromal stage of Alzheimer's disease, we examined whether the brain system for associative-semantic judgments with words or with pictures is affected and how this relates to off-line chronometric analysis of word reading and picture naming. A consecutive memory clinic-based series of 13 amnestic MCI patients as well as 13 matched controls participated. One area, the lower bank of the posterior third of the left superior temporal sulcus (STS), showed a significant group-by-task interaction: In controls, it was activated during the associative-semantic condition with words compared with the visuoperceptual control condition but not when the same tasks were compared with pictures as input. In MCI, this word-specific activation was significantly reduced. Response amplitude correlated (r = 0.90) with the steepness of the slope of the time-accuracy curve for word reading. Our data provide converging evidence for a critical contribution of the lower bank of the left posterior STS to mapping word form onto word meaning (lexical-semantic retrieval).

Evaluative conditioning is intact after unilateral resection of the anterior temporal lobe in humans

Several lesion and functional imaging studies conducted in animals and humans suggest that structures within the amygdaloid nuclear complex (ANC) are important for the occurrence of fear conditioning. Whether this brain structure is also critical for evaluative conditioning, has been investigated less frequently. In the current experiment, a group of participants with unilateral resection of the anterior temporal lobe and a control group received a differential evaluative flavor-taste conditioning task. In the pre-acquisition phase, two fruit flavors (the conditioned stimuli (CSs)) were presented and participants were instructed to evaluate both. In the subsequent acquisition phase, one of these fruit flavors (CS+) was presented together with a bad tasting substance Tween20 (polysorbate 20, the US), while the other flavor (CS-) was never paired with Tween20. Finally, in the post-acquisition phase, the two flavors were presented again without Tween20 and participants were asked to evaluate both of them for a last time. The control group as well as the lesion group rated the CS+ in the post-acquisition phase less favorable than in the pre-acquisition phase, while the ratings of the CS- remained the same in both phases. We clearly demonstrated evaluative conditioning in both test groups. Because the lesion group had still one intact ANC it would be premature, however, to conclude that the ANC is not involved in evaluative conditioning. We conclude that despite evidence for impaired fear conditioning, unilateral damage to the ANC does not impair evaluative conditioning.

Attentional responses to unattended stimuli in human parietal cortex

Right-sided parietal lesions lead to lateralized attentional deficits which are most prominent with bilateral stimulation. We determined how an irrelevant stimulus in the unattended hemifield alters attentional responses in parietal cortex during unilateral orienting. A trial consisted of a central spatial cue, a delay and a test phase during which a grating was presented at 9 degrees eccentricity. Subjects had to discriminate the orientation of the grating. The unattended hemifield was either empty or contained a second, irrelevant grating. We carried out a series of functional MRI (fMRI) studies in 35 healthy volunteers (13 men and 22 women, aged between 19 and 30 years) as well as a behavioural and structural lesion mapping study in 17 right-hemispheric lesion patients, 11 of whom had neglect. In the patients with but not in those without neglect, the addition of a distractor in the unattended hemifield significantly impaired performance if attention was directed contralesionally but not if it was directed ipsilesionally. In the healthy volunteers, we discerned two functionally distinct areas along the posterior-anterior axis of the intraparietal sulcus (IPS). The posterior, descending IPS segment in both hemispheres showed attentional enhancement of responses during contralateral attentional orienting and was unaffected by the presence of an irrelevant stimulus in the ignored hemifield. In contrast, the right-sided horizontal IPS segment showed a strong attentional response when subjects oriented to a stimulus in the relevant hemifield and an irrelevant stimulus was simultaneously present in the ignored hemifield, compared with unilateral stimulation. This effect was independent of the direction of attention. The symmetrical left-sided horizontal IPS segment showed the highest responses under the same circumstances, in combination with a contralateral bias during unilateral stimulation conditions. None of the six patients without neglect had a lesion of the horizontal IPS segment. In four of the 11 neglect patients, the lesion overlapped with the horizontal IPS activity cluster and lay in close proximity to it in another four. The remaining three patients had a lesion at a distance from the parietal cortex. Our findings reconcile the role of the IPS in endogenous attentional control with the clinically significant interaction between direction of attention and bilateral stimulation in right parietal lesion patients. Functional imaging in neglect patients will be necessary to assess IPS function in those cases where the structural lesion spares the middle IPS segment.

Paradoxical features of word finding difficulty in primary progressive aphasia

Impaired word retrieval is a main symptom of primary progressive aphasia (PPA). The cognitive features of this impairment in PPA are poorly understood. We studied 12 patients with PPA (6 English-speaking and 6 Dutch-speaking), 7 patients with early-stage clinically probable Alzheimer's disease (PRAD), 5 patients with mild cognitive impairment (MCI), and 15 age-matched, cognitively intact, control subjects. Subjects had to name a picture (the probe), which was preceded by a written word (the prime) that could be the correct name of the picture, a noun belonging to the same semantic subcategory (related prime), a semantically unrelated noun (unrelated prime), or a pseudoword (neutral control). Naming latencies were longer in PPA and PRAD patients than in control subjects. Critically, the interaction between group and prime type was highly significant. PPA patients named the probe more slowly after a related compared with an unrelated prime. In contrast, PRAD patients, mild cognitive impairment patients, and healthy control subjects tended to name the probe faster when it was preceded by a related prime. The semantic interference effect in PPA generalized across languages and PPA subtypes. Selection among competing word forms sharing a same semantic field is abnormal in PPA. The semantic interference effect constitutes a positive distinguishing feature between PPA and PRAD.

Anterior temporal laterality in primary progressive aphasia shifts to the right

In aphasia due to stroke, language-related activity shifts not only to undamaged cortex within the dominant hemisphere but also toward right-sided areas homotopical to the left-sided lesion. We examined whether a rightward shift takes place in primary progressive aphasia (PPA). Nineteen PPA patients participated, 19 healthy subjects and 14 patients with amnestic mild cognitive impairment who served as controls. Subjects underwent neuropsychological assessment, structural magnetic resonance imaging (MRI), and a functional MRI with a factorial design: words versus pictures and associative-semantic versus visuoperceptual task. Measures of neuropsychological performance were entered as regressors into a multiple linear regression analysis, with response amplitude during the associative-semantic versus control conditions as outcome variable. Language competence correlated negatively with responses in the right anterior temporal cortex and positively with volume and responses in the left-sided homotope. In normal subjects, anterior temporal activation was more extensive to the left than the right (laterality index [LI], +0.64; standard error [SE], 0.11). Laterality was inverted in PPA with word comprehension deficit (LI, - 0.34; SE, 0.19), with an intermediate pattern in PPA without comprehension deficit (LI, +0.23; SE, 0.14). The rightward laterality shift previously reported in aphasic stroke extends to PPA, in particular, when comprehension is deficient.

Acute axonal polyneuropathy in chronic alcoholism and malnutrition

In contrast to the classic, slowly progressive polyneuropathy in alcoholic patients, acute forms, clinically mimicking Guillain-Barré syndrome, are rare. We present a patient who developed motor weakness and sensory loss in all four limbs within four days. Laboratory data were consistent with long-term alcohol abuse and documented thiamine deficiency. Repeated cerebrospinal fluid examinations were normal. Electrophysiological studies showed an acute sensorimotor polyneuropathy with predominantly axonal involvement. We conclude that acute alcoholic neuropathy has to be distinguished from Guillain-Barré syndrome and other forms of acute polyneuropathy by using clinical, laboratory, and electrophysiological data. Both ethanol toxicity and vitamin deficiency could play a role in the pathogenesis.