The effect of apomorphine and buspirone on regional cerebral blood flow during the performance of a cognitive task-measuring neuromodulatory effects of psychotropic drugs in man

Assessing the efficacy and safety of combined buspirone and venlafaxine treatment in late-life depression accompanied by cognitive impairment: A randomized controlled trial

BACKGROUND

Late-life depression, often accompanied by cognitive impairment, poses significant clinical challenges owing to its complex etiology and diverse manifestations. While antidepressants like venlafaxine and anxiolytics such as buspirone are effective for treating depression, their effects on cognitive function remain less well-understood. With the aging population increasingly experiencing geriatric depression, there is an urgent need for innovative treatment approaches that address both depressive symptoms and cognitive impairments.

OBJECTIVE

This study aimed to evaluate the clinical efficacy and safety of combined buspirone and venlafaxine therapy in elderly patients diagnosed with geriatric depression accompanied by cognitive impairment.

METHODS

A 12-week, randomized controlled trial was conducted involving 170 elderly patients. Participants were randomized into two groups: one receiving venlafaxine alone (control group) and the other receiving a combination of venlafaxine and buspirone (experimental group). The primary analysis was performed using an Intent-to-Treat (ITT) approach with mixed-effects linear models to assess changes in depressive symptoms, cognitive function, and anxiety levels. A supplementary Per-Protocol (PP) analysis, utilizing repeated measures ANOVA, was also conducted.

RESULTS

The ITT analysis showed that the combination therapy significantly reduced depressive symptoms, as indicated by the HAMD-17 scores (p = 0.033 at week 12). Cognitive function, as measured by MoCA scores, also improved significantly in the experimental group by week 12 (p = 0.025). However, no statistically significant differences were observed in anxiety reduction between the groups (p = 0.127). The PP analysis confirmed these findings, demonstrating consistent improvements in depressive symptoms and cognitive function, particularly in those who completed the full course of treatment. The incidence of adverse events was comparable between groups, primarily mild and manageable symptoms like dry mouth, dizziness, and fatigue.

CONCLUSION

The combination of buspirone and venlafaxine was found to be effective in reducing depressive symptoms and enhancing cognitive function in elderly patients with geriatric depression. However, the long-term benefits, especially regarding anxiety reduction, require further investigation. Future studies should consider larger sample sizes, longer follow-up periods, and the inclusion of placebo controls to fully assess the efficacy and safety of this treatment approach.

Cognitive Dysfunction in Parkinson’s Disease: The Role of Frontostriatal Circuitry

It has been known for many years that the classic motor symptoms of Parkinson’s disease are accompanied by deficits of executive function that resemble those seen after frontal lobe damage in humans. What is less clear is how different components of frontostriatal circuitry contribute to these impairments. Recently, improved methods of clinical assessment and classification, combined with novel technical approaches, such as functional neuroimaging, have led to great advances in our understanding of the fundamental mechanisms that drive frontostriatal circuitry. As a direct result, it has been possible to redefine impairments of executive function in Parkinson’s disease more precisely in terms of the specific neuropsychological, neuroanatomical, and psychopharmacological mechanisms involved.

Drug targets for cognitive enhancement in neuropsychiatric disorders

The investigation of novel drug targets for treating cognitive impairments associated with neurological and psychiatric disorders remains a primary focus of study in central nervous system (CNS) research. Many promising new therapies are progressing through preclinical and clinical development, and offer the potential of improved treatment options for neurodegenerative diseases such as Alzheimer's disease (AD) as well as other disorders that have not been particularly well treated to date like the cognitive impairments associated with schizophrenia (CIAS). Among targets under investigation, cholinergic receptors have received much attention with several nicotinic agonists (α7 and α4β2) actively in clinical trials for the treatment of AD, CIAS and attention deficit hyperactivity disorder (ADHD). Both glutamatergic and serotonergic (5-HT) agonists and antagonists have profound effects on neurotransmission and improve cognitive function in preclinical experiments with animals; some of these compounds are now in proof-of-concept studies in humans. Several histamine H3 receptor antagonists are in clinical development not only for cognitive enhancement, but also for the treatment of narcolepsy and cognitive deficits due to sleep deprivation because of their expression in brain sleep centers. Compounds that dampen inhibitory tone (e.g., GABA(A) α5 inverse agonists) or elevate excitatory tone (e.g., glycine transporter inhibitors) offer novel approaches for treating diseases such as schizophrenia, AD and Down syndrome. In addition to cell surface receptors, intracellular drug targets such as the phosphodiesterases (PDEs) are known to impact signaling pathways that affect long-term memory formation and working memory. Overall, there is a genuine need to treat cognitive deficits associated with many neuropsychiatric conditions as well as an increasingly aging population.

Neurocognitive costs and benefits of psychotropic medications in older adults

Psychotropic medications are widely used in older adults and may cause neurocognitive deficits. Older adults are at increased risk of developing adverse effects because of age-related pharmacodynamic and pharmacokinetic changes. This article provides a comprehensive review of the undesirable, and at times beneficial, effects of psychotropic medications. The review covers a wide range of medications that impair executive function, memory, and attention, as well as a much smaller group of medications that lead to improved neurocognitive function. Some of the most commonly used psychotropic medications in older adults, namely, antidepressants, sedatives, and hypnotics, are among the drugs that most consistently lead to cognitive impairments. Medications with anticholinergic properties almost invariably lead to neurocognitive dysfunction, despite symptom improvement. The neurocognitive costs and benefits of psychiatric medications should be considered in the context of disease treatment in older adults.

Lack of deleterious effects of buspirone on cognition in healthy male volunteers

Buspirone is a serotonin 5-HT(1A) receptor agonist licensed for the treatment of anxiety. Other anxiolytic drugs such as benzodiazepines show significant sedative and other unwanted effects on cognition. Studies to date have yet to investigate cognitive effects of buspirone using well-validated computerized tests. The aim of this study was to assess acute subjective and cognitive effects of buspirone in healthy volunteers. Sixty healthy male volunteers received 20 mg buspirone, 30 mg buspirone, or placebo per os in a double-blind parallel groups design (N=20 per group). Subjective ratings (visual analogue scales) were completed at baseline, and at 1.5 and 3.5 hours post-capsule. Cognitive assessment was undertaken between 1.5 and 3.5 hours post-capsule, including tests of memory, executive planning, impulse control, decision making and cognitive flexibility. The 30 mg buspirone group showed significantly higher subjective ratings of contentedness 3.5 hours after capsule relative to placebo. Treatment and placebo groups did not differ significantly on cognitive measures. In contrast to benzodiazepines, the anxiolytic buspirone appears to lack detectable deleterious effects on cognition when administered acutely at clinically meaningful doses. Future research directions are discussed in relation to acute and chronic studies in neuropsychiatric populations.

Positron emission tomography and single-photon emission computed tomography in central nervous system drug development

In this review, the value of functional imaging [positron emission tomography (PET)/single-photon emission computed tomography (SPECT)] in drug development is considered. Radionuclide imaging can help establish the diagnosis of neurodegenerative disorders where this is in doubt and provides a potential biomarker for following drug effects on disease progression. PET and SPECT can help understand mechanisms of disease and determine the functional effects of therapeutic approaches on neurotransmission and metabolism. Synthesizing radiotracer analogs of novel drugs can provide proof of principle that these agents reach their enzyme or receptor targets and delineate their regional brain distribution. If such radiotracers do not prove to have ideal properties for imaging, the concept of microdosing potentially allows multiple other drug analogs to be tested with less stringent regulatory requirements than for novel medicinals. Finally, PET tracers can provide receptor and enzyme active site dose occupancy profiles, thereby guiding dosage selection for phase 1 and phase 2 trials. The eventual hope is that radiotracer imaging will provide a surrogate marker for drug efficacy, although this has yet to be realized, and progress the concept of personalized medicine where receptor/enzyme binding profiles help predict therapeutic outcome.

Distributed neural actions of anti-parkinsonian therapies as revealed by PET

There is a limited understanding of how different anti-parkinsonian treatments act at the neuronal systems level. Using positron emission tomography we examined the effects of levodopa and deep brain stimulation of the subthalamic nucleus on patterns of regional cerebral blood flow in patients with Parkinson's disease during a homogenous cognitive-behavioural state rather than during an unspecified resting state. We found that when medicated precuneus, frontal, parietal, cerebellar and midbrain areas were relatively more activated than when stimulated, whereas when stimulated the precentral gyrus, caudate and thalamus were relatively more activated than when medicated. Areas that were activated by both treatments included the temporal gyri, anterior thalamus, and midbrain. Regions of prefrontal cortex showed relatively greater activation in the "off treatment" conditions of both the medicated and stimulated groups. Our findings suggest that the two treatment methods may lead to symptomatic relief via both common and different sites of action.

Impact of apomorphine on BOLD signal during movement in normals

Our group investigated modulatory effects of apomorphine on cerebral activation patterns during finger tapping movements in six healthy right-handed volunteers using an established fMRI protocol. Apomorphine application disclosed a reduction of cerebral activation to the contralateral precentral and postcentral gyrus and ipsilateral cerebellum, with a prominent net reduction of BOLD signal in cerebellar areas. These findings contradict those of similar studies performed on dopaminergic function and Parkinson's disease (PD), which predominantly found augmentation of cerebral activation patterns in normal volunteers and PD patients after dopaminergic stimulation. One conceivable explanation for our singular results would be preferred binding of apomorphine to presynaptic dopaminergic receptors, leading to inhibition of endogenous dopamine release and resultant diminished dopaminergic stimulation, reflected in diminished cerebral activation patterns. These findings warrant future consideration and further investigation of possible central inhibitory effects of dopaminergic therapy in functional imaging studies of the dopaminergic system in general and PD in particular.

Effects of acute tryptophan depletion on executive function in healthy male volunteers

BACKGROUND

Neurocognitive impairment is frequently described in a number of psychiatric disorders and may be a direct consequence of serotonergic dysfunction. As impairments in executive functions are some of the most frequently described, the purpose of this study was to examine the performance of normal volunteers on a range of executive tasks following a transient reduction of central serotonin (5-HT) levels using the method of acute tryptophan depletion (ATD).

METHODS

Fifteen healthy male subjects participated in a within-subject, double-blind, counterbalanced crossover study. ATD was induced by ingestion of a 100 g amino-acid drink. Executive function was evaluated using the Wisconsin Card Sorting Test, Stroop, Verbal Fluency and Trail Making. Visual analogue scales were administered to assess mood.

RESULTS

Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001). ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood. Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

CONCLUSIONS

The improvement in simple motor speed/ attention following ATD is in keeping with the ascribed role of 5-HT in the cortex, however performance on tests of executive function is not robustly altered. The presence of interaction effects on most tasks suggests that subtle changes may occur but are masked, possibly by simple learning effects, in the context of a crossover design. This has implications for the design of future studies, particularly those examining executive functions.

Disruption of information processing in the supplementary motor area of the MPTP-treated monkey: a clue to the pathophysiology of akinesia?

It has been suggested that the underactivity of mesial frontal structures induced by dopamine depletion could constitute one of the main substrates underlying akinesia in Parkinson's disease. Functional imaging and movement-related potential recordings indicate an implication of the frontal lobes in this pathological process, but the question has not yet been investigated at a cellular level using single unit recording. We therefore compared neuronal activity in both the presupplementary motor area (pre-SMA) and the supplementary motor area proper (SMAp) of the Macaca mulatta monkey during a delayed motor task, before and after MPTP treatment. In the pre-SMA, which receives strong inputs from the prefrontal cortex, the baseline firing frequency and the percentage of neurons responding to visual instruction cues decreased in lesioned monkeys. In the SMAp, which sends direct outputs to the primary motor cortex, not only was the response to visual cues impaired, but the percentage of SMAp neurons responding to intracortical microstimulation fell and the threshold of response rose. Neuronal activity after the Go signal diminished sharply in both structures in the symptomatic animal and the discharge pattern became more irregular; in the SMAp neuronal activity remained modified longer. Most of these changes could already be observed in the presymptomatic animal presenting no clinical signs of parkinsonism. These data would indicate that, at the moment when dopamine depletion has impaired the ability of cortical neurons to operate the focused selection of incoming information giving instructions for movement, pre-SMA and SMAp neurons are also in a state of severe hypoactivity. The conjunction of these phenomena could play a critical role in the genesis of akinesia.

Dopaminergic modulation of high-level cognition in Parkinson's disease: the role of the prefrontal cortex revealed by PET

This study examined the effects of L-dopa medication in patients with Parkinson's disease on cortical and subcortical blood flow changes during two tasks known to involve frontostriatal circuitry. Eleven patients with Parkinson's disease were scanned on two occasions, one ON L-dopa medication and one OFF L-dopa medication, during performance of the Tower of London planning task and a related test that emphasized aspects of spatial working memory. L-dopa-induced decreases were observed in the right dorsolateral prefrontal cortex during performance of both the planning and the spatial working memory tasks compared with the visuomotor control task. Conversely, L-dopa-induced blood flow increases were observed in the right occipital lobe during the memory task relative to the control task. Data from age-matched healthy volunteers demonstrated that L-dopa effectively normalized blood flow in these regions in the patient group. Moreover, a significant correlation was found between L-dopa-induced, planning related blood flow decreases in the right dorsolateral prefrontal cortex and L-dopa-induced changes in performance on the planning task. These data suggest that L-dopa ameliorates high-level cognitive deficits in Parkinson's disease by inducing relative blood flow changes in the right dorsolateral prefrontal cortex.

Effects of tryptophan loading on verbal, spatial and affective working memory functions in healthy adults

Serotonin (5-HT) appears to modulate affective behaviours by providing a homeostatic threshold around which other transmitters respond. This general principle of activity should hold for other types of behaviour, including cognition, but has not been extensively examined. We hypothesized, based on past findings, that increased 5-HT would constrain prefrontally guided working memory functions that are mediated by catecholamine neurotransmitters. Healthy adults ingested amino acid compounds designed to deplete and load systemic tryptophan levels in a repeated-measures crossover design. Outcome variables included total plasma tryptophan, serum prolactin levels and self-report measures of mood, as well as measures of motor skill, attention, memory span and working memory for verbal, spatial and affective stimuli. Our findings indicate decrements in working memory for verbal and affective stimuli following tryptophan loading versus depletion, as well as subtle changes in vigilant attention and motor coordination. Implications for the aetiology and treatment of affective disorders and psychosis are discussed.

Acute effect of 3-(4-acetamido)-butyrril-lorazepam (DDS2700) on brain function assessed by PET at rest and during attentive tasks

The aim of this study was to assess, by positron emission tomography (PET), the effect on cerebral functional activity of a new lorazepam-gamma-aminobutyric acid (GABA) conjugate [3-(4-acetamido)-butyrril lorazepam (DDS2700)]. Ten healthy volunteers were studied by PET and [18F]fluoro-deoxy-D-glucose ([18F]FDG) under baseline conditions and following the administration of DDS2700. Regional cerebral blood flow (rCBF) was measured by PET and 15O-water in three additional participants while they performed attentive tasks, before and after drug administration. DDS2700 induced a decrease in the regional cerebral metabolic rate of glucose (rCMRglu) in the thalamus (-17%), cerebellum (-11%) and caudate nucleus (-8%). The observed effects on glucose metabolism were probably related to the subjective sedation and tiredness reported by the participants. During the attentive tasks, rCBF increased in frontal and temporal regions associated with attentional processing of auditory material. These circuits were no longer active after DDS2700 administration, while rCBF increased in cingulate cortex, occipitoparietal regions, pons and cerebellum. These drug-induced activations might be directly related to intervening sleepiness and to the consequent effort in keeping attention focused on the tasks. The effects of DDS2700 on glucose metabolism at rest, and on rCBF during activation conditions, indicate a drug action on cerebral networks involved in alertness, vigilance and attention maintenance. PET assessment by [18F]FDG and water may provide complementary information in pharmacodynamic studies.

Neuroscience. Boosting working memory

Working out which areas of the brain become activated during the formation of working (short-term) memory has been greatly helped by functional magnetic resonance imaging (fMRI). In a Perspective, Robbins et al. discuss new findings (Furey et al.) with fMRI that reveal how working memory is enhanced by the drug physostigmine, which increases cholinergic function in the brain.

Abnormal neural integration related to cognition in schizophrenia

A striking feature of schizophrenia is the diversity of the phenomenology both within and between patients. This diversity can be contrasted with the well-circumscribed and stable deficits seen in classic neuropsychological syndromes. The argument will be advanced that the classic lesion model, based on the notion of a segregated deficit, is inappropriate in schizophrenia. Instead the idea will be developed that a more appropriate model is one derived from concepts of neural integration across large-scale brain networks. Empirical data derived from positron emission tomography (PET) within our laboratory that provide support for this suggestion will be presented. One critical observation from these data is a disruption of prefrontal-temporal interactions, under a variety of cognitive activation paradigms, in both chronic medicated and acute unmedicated schizophrenic patients. Furthermore, these data indicate that both regional and interregional neuronal function, including prefrontal-temporal interactions, can be significantly modulated by a neurochemical perturbation of ascending dopaminergic systems. The latter observations suggest that the deficit of abnormal cortico-cortical interactions are to some extent modifiable by neuromodulatory neurotransmitter systems.

Arousal systems and attentional processes

Unitary concepts of arousal have outlived their usefulness and their psychological fractionation corresponds to a similar chemical differentiation of the reticular formation of the brain. Neurobiological characteristics of the monoaminergic and cholinergic systems can be described in terms of their anatomical, electrophysiological and neurochemical properties. Functional studies suggest that the coeruleo-cortical noradrenergic system, under certain circumstances, is implicated in processes of selective attention, that the mesolimbic and mesostriatal dopaminergic systems contribute to different forms of behavioural activation, and that the cortical cholinergic projections have fundamental roles in the cortical processing of signals, affecting attentional and mnemonic processes. The ascending serotoninergic systems contribute to behavioural inhibition and appear to oppose the functions of the other systems in several ways.

The neural correlates of the noradrenergic modulation of human attention, arousal and learning

The prefrontal cortex has been suggested as a site of action for the noradrenergic modulation of cognition. In healthy volunteers attentional deficits can be induced by the alpha 2 adrenoceptor agonist clonidine, without impairment of more explicit tests of frontal lobe function. It is therefore possible that the effects of noradrenaline cannot be localized to a specific brain area such as the prefrontal cortex, but instead involve structures in a more widespread attentional network. A 1.5 micrograms/kg dose of clonidine or placebo was administered to 13 healthy male volunteers performing the rapid visual information processing task, which places demands on both sustained attention and working memory. Twelve positron emission tomography measurements of regional cerebral blood flow (rCBF) were collected during performance of this task and also during a rest state. A second experiment in 12 healthy volunteers examined the effects of a 1.3 micrograms/kg dose of clonidine on the rCBF changes associated with performance of a paired associates learning task compared with passive listening to word pairs. Comparison of each of the experimental tasks with its respective control replicated previous findings. A significant drug x task interaction, common to the two studies, was found in the right thalamus. Inspection of the adjusted rCBF values showed that the effect was due to attenuation of thalamic rCBF during the control states rather than to any effects of clonidine during performance of the cognitive tasks, although the effect was stronger in the rapid visual information processing study than in the paired associates learning study. The significant effect of clonidine during the control as opposed to the "cognitive' activation state is consistent with previous findings in animals and humans demonstrating greater effects of clonidine during states of relatively low arousal. The results suggest neuroanatomical dissociation of the noradrenergic modulation of arousal (via the thalamus) and attention.

Local and distributed effects of apomorphine on fronto-temporal function in acute unmedicated schizophrenia

We used positron emission tomography (PET) to measure brain activity in healthy control subjects and unmedicated patients with schizophrenia. Subjects were scanned in the context of a combined psychological and pharmacological challenge, and we examined the effects of apomorphine, a drug acting on dopamine receptors, on brain systems engaged by a paced verbal fluency task. This factorial design enabled comparison of control subjects and schizophrenics in terms of the activations engendered by the cognitive task and the pharmacological challenge and the interaction of the two. We report a failure of cognitive task-related activation in anterior cingulate cortex and of task-related deactivation in the left superior temporal gyrus in the schizophrenic subjects. Compared with controls, the impaired cingulate activation was significantly reversed by apomorphine. Additionally, there was a trend for the abnormal fronto-temporal pattern of activation in schizophrenic subjects to be normalized by the drug. Overall, in schizophrenic subjects the effect of apomorphine, which we interpret in terms of a net dopaminergic antagonism, was to modify the brain activity, making the pattern more akin to that seen in control subjects. The results indicate both a regionally specific abnormality of brain function in schizophrenia and an abnormal pattern of fronto-temporal interactions.

Cerebral metabolic effects of serotonin drugs and neurotoxins

The functional effects of serotonin (5-HT) drugs and toxins on regional cerebral metabolic rates for glucose (rCMRglc) have been determined in rats with the in vivo, quantitative, autoradiographic [14C]2-deoxyglucose technique. Serotonin agents produced rCMRglc patterns different and more specific that one would predict from binding studies. At low doses 5-HT1 agonists reduced rCMRglc in limbic areas and at high doses increased rCMRglc in brain motor regions. The 5-HT2 agonists dose-dependently decreased rCMRglc in proencephalic areas and increased it in thalamic nuclei. 5-HT3 receptor antagonism resulted in rCMRglc decreases in limbic, auditory and visual areas and agents with 5-HT3 receptor activity increased rCMRglc in brain regions with high 5-HT3 receptor densities. Serotonin anxiolytics (e.g. azapirones) and antidepressants (e.g. tryciclic and non-tryciclic 5-HT reuptake inhibitors) reduced rCMRglc selectively in limbic areas and in brainstem monoaminergic nuclei. Dose, time from administration, receptor affinity, behavioral and neurochemical correlates, 5-HT system lesion and circulating glucocorticoid were all relevant factors in determining the rCMRglc effects of 5-HT drugs. Acutely neurotoxic amphetamines markedly increased rCMRglc in brain regions such as the nucleus accumbens that are thought to mediate amphetamine reinforcing properties; on the long term, toxic or electrolytic lesions or chronic treatment with 5-HT agonists produced minimal rCMRglc alterations in spite of marked and persistent changes in 5-HT function. In lesioned or chronically treated rats, acute challanges with 5-HT and non 5-HT agonists demonstrated specific deficits that were not detected in a resting state. Serotonin neuromodulation has been studied in humans by using positron emission tomography with 15O-water. Sequential measurements of regional cerebral blood flow (rCBF) were obtained during combined pharmacological challange with the 5-HT1A agonist buspirone and cognitive activation. Buspirone increased a memory related rCBF activation in task specific regions. This technique can provide a strong theoretical basis for the understanding of 5-HT drug mode of action in normal human brain and in neuropsychiatric diseases. Brain metabolism studies in animals will still be needed to elucidate the factors (e.g. pharmacokinetic and pharmacodynamic) relevant to the cerebral response to 5-HT drugs in humans.

The effect of the muscarinic antagonist scopolamine on regional cerebral blood flow during the performance of a memory task

Scopolamine, a muscarinic antagonist, impairs memory performance in both humans and animals. In this study, repeated measurements of regional cerebral blood flow (rCBF) were made in normal volunteers whilst performing auditory verbal memory tasks, before and after the administration of scopolamine (0.4 mg s.c.) or placebo. Compared to placebo, scopolamine increased blood flow in the lateral occipital cortex bilaterally and the left orbitofrontal region. Scopolamine decreased rCBF in the region of the right thalamus, the precuneus and the right and left lateral premotor areas. Scopolamine attenuated memory-task-induced increases of rCBF in the left and right prefrontal cortex and the right anterior cingulate region. These data suggest that acute blockade of cholinergic neurotransmission affects diverse brain areas, including components of the visual and motor systems, and, in addition, modulates memory task activations at distinct points in a distributed network for memory function.

Benzodiazepine receptors mediate regional blood flow changes in the living human brain

We studied the effects of a high-affinity gamma-aminobutyric acid (GABA)-benzodiazepine-receptor agonist (lorazepam) and an antagonist (flumazenil) in humans, using H2(15)O positron-emission tomography. Administration of lorazepam to healthy volunteers caused time- and dose-dependent reductions in regional cerebral blood flow and self-reported alterations in behavioral/mood parameters. Flumazenil administration reversed these changes. These observations indicated that benzodiazepine-induced effects on regional cerebral blood flow and mood/behavior are mediated at some level through GABA-benzodiazepine receptors, although the specific mechanism remains unclear. The approach described here provides a method for quantifying GABA-benzodiazepine-receptor-mediated neurotransmission in the living human brain and may be useful for studying the role of these receptors in a variety of neuropsychiatric disorders.

Decreased cingulate and precuneate glucose utilization in alcoholic Korsakoff's syndrome

Localized cerebral glucose utilization was determined for nine abstinent alcoholic men with Korsakoff's syndrome and 10 age-matched normal men who underwent positron emission tomography with [18F]2-fluoro-2-deoxyglucose (FDG). Patients with Korsakoff's syndrome showed relatively decreased glucose utilization in cingulate and precuneate areas. These decreases persisted even after correction for group differences in ventricular and sulcal cerebrospinal fluid measured on computed tomography. Electroencephalographic recordings at the time of FDG uptake showed no group differences, a finding that demonstrates that the metabolic differences could not be explained by differences in physiological arousal at the time of scanning. It is concluded that the decreased glucose utilization in the patients reflects a disruption of memory circuitry, the Papez circuit, caused by diencephalic lesions induced by thiamine deficiency.

Imaging transient, randomly occurring neuropsychological events in single subjects with positron emission tomography: an event-related count rate correlational analysis

Many neuropsychiatric symptom states are idiosyncratic, involuntary, randomly occurring, subjective, and transient. The brain states associated with these clinically important mental states cannot be imaged directly with existing positron emission tomography (PET) techniques. A new PET method that brings such mental/brain states under experimental control for analysis in single subjects is described. It utilizes a slow bolus H2 15O three-dimensional (3D) regional CBF imaging technique. The analysis focuses upon natural or experimentally induced variance in the temporal distribution of specific neuropsychological events over the course of a study session. For each scan, the amount of radioactivity entering the brain during these events is calculated to derive a score reflecting the contribution of the events to the image. A statistical analysis is then performed to identify those pixels in which the intensity covaries with the scan scores over the subject's scans. This permits the identification of the brain areas associated with the mental state of interest. The method is validated using an auditory sentence-monitoring task. The detection in single subjects of cerebral activations associated with recurrent events as brief as 2 s in duration is demonstrated. This method may be used as a means of imaging ephemeral neurologic or neuropsychiatric symptom states or as an alternative to a subtraction design for activation studies.

Tryptophan depletion in normal volunteers produces selective impairments in learning and memory

The amino-acid L-tryptophan is essential in the synthesis of brain serotonin, and its depletion can lead to a widespread reduction in central serotonergic activity. A placebo-controlled cross-over within-subjects design (n = 12) examined the effects of tryptophan depletion on human cognitive performance. A low-tryptophan (low-TRP) drink successfully reduced the levels of plasma and total free tryptophan. Computerized tests of memory, learning and executive function revealed selective and non-sedative impairments on cognitive performance following the active drink. Specifically, low-TRP impaired learning as seen in tests of visual discrimination and paired associates. Furthermore, low-TRP lengthened thinking times during the Tower of London planning task, but only in subjects already familiar with the task, suggesting a retrieval deficit. No evidence was found for an effect of the low-TRP drink on measures sensitive to frontal lobe dysfunction, supporting instead a specific role for the serotonergic system in the processes of memory and learning not directly implicated in frontal lobe function.