Inflexibility of mental planning: a characteristic disorder with prefrontal lobe lesions?

Exploring behavioural and cognitive dysexecutive syndrome in patients with focal prefrontal cortex damage

This study's objectives were to characterize the frequency and profile of behavioral and cognitive dysexecutive syndromes in patients with focal prefrontal cortex damage and how these syndromes overlap. We also examined the contribution of the prefrontal brain regions to these syndromes. Therefore, thirty patients with prefrontal cortex damage and thirty control subjects were compared on their performances using the GREFEX battery assessing the dysexecutive syndromes. The results showed that combined behavioral and cognitive dysexecutive syndrome was observed in 53.33%, while pure cognitive dysexecutive syndrome was observed in 20% and behavioral in 26.67%. Also, almost all behavioral and cognitive dysexecutive disorders discriminated frontal patients from controls. Moreover, correlations and regression analyses between task scores in both domains of dysexecutive syndromes showed that the spectrum of behavioral disorders was differentially associated with cognitive impairment of initiation, inhibition, generation, deduction, coordination, flexibility and the planning process. Furthermore, the patterns of cognitive and behavioral dysexecutive syndrome were both predictors of impairment in daily living activities and loss of autonomy. Finally, frontal regions contributing to different dysexecutive syndromes assessed by MRI voxel lesion symptom analysis indicate several overlapping regions centered on the ventromedial and dorsomedial prefrontal cortex for both domains of dysexecutive syndrome. This study concludes that damage to the frontal structures may lead to a diverse set of changes in both cognitive and behavioral domains which both contribute to loss of autonomy. The association of the ventromedial and dorsomedial prefrontal regions to both domains of dysexecutive syndrome suggests a higher integrative role of these regions in processing cognition and behavior.

The Effect of Donepezil on Problem-solving Ability in Individuals With Amnestic Mild Cognitive Impairment: A Pilot Study

BACKGROUND

Clinical trials involving individuals with mild cognitive impairment (MCI) have reported mixed results for the effects of cholinesterase inhibitors on cognitive outcomes. Our previous work demonstrated that a visuospatial problem-solving task was sensitive to non-memory impairments in individuals with MCI.

OBJECTIVE

To determine whether the same task is also sensitive to the effects of cholinesterase inhibitors in individuals with amnestic MCI (aMCI).

METHOD

We gave 22 individuals with aMCI (clinical dementia rating of 0.5) and Mini-Mental State Examination (MMSE) scores of at least 24 the following measures at baseline and at follow-up 1 year later: Hopkins Verbal Learning Test, Boston Naming Test, Rey Complex Figures Test copying task, anagrams task, and visuospatial problem-solving task. The MMSE was also given at the 1-year follow-up. Twelve of the individuals were drug naïve, having never taken cholinesterase inhibitors before, and donepezil was initiated and titrated to 10 mg daily after baseline in an open-label manner. Ten of the individuals had already been taking donepezil, and there was no change in treatment. We compared the two groups for amount of performance change over 1 year.

RESULTS

Individuals for whom donepezil was initiated performed significantly better on the visuospatial problem-solving task after 1 year compared with individuals who had already been taking donepezil. No difference was observed for any of the other variables.

CONCLUSION

The visuospatial problem-solving task appeared to be more sensitive than memory measures to the effects of cholinesterase inhibitors in individuals with aMCI, perhaps due to the high attentional demand of the task.

The Role of the Noradrenergic System in Autism Spectrum Disorders, Implications for Treatment

Autism spectrum disorder (ASD) is frequently associated with anxiety and hyperarousal. While the pathological changes in the noradrenergic system in ASD are not entirely clear, a number of functional indices of the sympathetic/parasympathetic balance are altered in individuals with ASD, often with a high degree of inter-individual variability. The neuropsychopharmacological effects of α₂ agonists and β-adrenergic antagonists make agents targeting these receptors of particular interest. α₂ agonists have shown beneficial effects for attention deficit hyperactivity disorder (ADHD) and in other domains in individuals with ASD, but effects on core ASD symptoms are less clear. Case series and single dose psychopharmacological challenges suggest that treatment with β-adrenergic antagonists has beneficial effects on language and social domains. Additionally, psychophysiological markers and premorbid anxiety may predict response to these medications. As a result, β-adrenergic antagonists are currently being utilized in a clinical trial for improving core symptoms as well as anxiety in individuals with ASD.

Relationship Between Cognitive-Behavioral Impairment and Clinical and Functional Parameters in ALS and Reliability of the Edinburgh Cognitive and Behavioural ALS Screen to Assess ALS: Preliminary Findings

BACKGROUND

Although it is widely recognized that a high percentage of individuals with amyotrophic lateral sclerosis (ALS) have cognitive and behavioral impairment, the associated clinical and functional parameters remain unknown. ALS is typically assessed via screening tests, such as the Edinburgh Cognitive and Behavioural ALS Screen (ECAS).

OBJECTIVE

To investigate the relationship between cognitive-behavioral impairment and other clinical and functional parameters and to compare the assessment results from a set of standardized neuropsychological tests with those from the ECAS.

METHODS

Forty individuals with ALS participated in the study. We assessed attention, memory and learning ability, and executive function using a set of standardized neuropsychological tests and the ECAS. Sociodemographic variables, time since onset of symptoms, time since diagnosis, and functional respiratory values were recorded.

RESULTS

No relationship was found between time since onset of symptoms and time since definitive diagnosis and either attention (P=0.206, 0.314, respectively), memory and learning ability (P=0.618, 0.692), or executive function (P=0.844, 0.583). The set of standardized neuropsychological tests identified an impairment in executive function in 29% of the participants, whereas the ECAS identified it in 89%.

CONCLUSIONS

We found no relationship between cognitive-behavioral impairment and time since onset of symptoms nor time since ALS diagnosis. Because the ECAS does not correctly reflect the executive function of individuals with ALS, function-specific neuropsychological tests are preferred. Test selection must take into account individuals' physical characteristics and their consequent ability to respond gesturally or orally.

Increased task difficulty results in greater impact of noradrenergic modulation of cognitive flexibility

Previous research suggests that the noradrenergic system modulates certain types of cognitive flexibility. This study compared various doses of beta-adrenergic antagonists for their effect on cognitive flexibility in problem solving, and how task difficulty interacts with this effect, as well as the effect of beta-adrenergic antagonists on other tasks. Anagram task performance was compared in 72 subjects using a within-subject design for propranolol at 20 mg, 40 mg, 60 mg, and placebo in a double-blinded manner, and the effects of subject ability and task difficulty were examined. We also examined the effect of the 40 mg propranolol dose on a range of other tasks. Overall, more anagram problems were solved while on propranolol 40 mg than on placebo. Subjects least able to solve the problems benefited significantly from 40 mg of propranolol. Also, for all subjects the most difficult problems were solved more quickly with propranolol 40 mg than placebo. Benefits were also seen for word fluency and backward digit span. Therefore, noradrenergic modulation of cognitive flexibility is affected by how much difficulty the subject is encountering when searching for the solution, a pattern consistent with what might be expected in an effect on the search of the semantic and associative network.

Problem Solving Ability in Patients With Mild Cognitive Impairment

BACKGROUND AND OBJECTIVE

It is important to determine which patients with mild cognitive impairment (MCI) are at risk for progression to dementia. The presence of mild impairments not restricted to the domain of memory may suggest such progression. Our goal is to determine how well a visuospatial problem solving task assessing the cumulative burden of frontal and posterior damage differentiates MCI patients from matched controls.

METHODS

Twenty-six patients with MCI [Clinical Dementia Rating (CDR) score of 0.5] and mini-mental state examination (MMSE) scores of at least 24/30, were compared with 20 age and education level matched controls without cognitive impairment. All patients were given the MMSE, Hopkins Verbal Learning Test (HVLT), Boston Naming Test (BNT), Rey Complex Figures copying (RCF), anagrams, and visuospatial problem solving battery (VPS). The VPS is a complex problem solving task, which we predicted would better discriminate patient groups than the relatively simpler tasks.

RESULTS

Differences existed between groups on most tasks, but logistic regression revealed that the VPS discriminated the 2 groups better than the other nonmemory cognitive tests.

CONCLUSIONS

The VPS, a problem solving task assessing the cumulative burden of frontal and posterior damage is more sensitive for detecting nonmemory impairments in MCI than other tasks. Future research will be needed to determine if impairment in the VPS is a sensitive predictor of progression to dementia or treatment response.

The "two-headed" latent inhibition model of schizophrenia: modeling positive and negative symptoms and their treatment

RATIONALE

Latent inhibition (LI), namely, poorer performance on a learning task involving a previously pre-exposed non-reinforced stimulus, is disrupted in the rat by the dopamine (DA) releaser amphetamine which produces and exacerbates psychotic (positive) symptoms, and this is reversed by treatment with typical and atypical antipsychotic drugs (APDs) which on their own potentiate LI. These phenomena are paralleled by disrupted LI in normal amphetamine-treated humans, in high schizotypal humans, and in schizophrenia patients in the acute stages of the disorder, as well as by potentiated LI in normal humans treated with APDs. Consequently, disrupted LI is considered to provide an animal model of positive symptoms of schizophrenia with face, construct and predictive validity.

OBJECTIVES

To review most of the rodent data on the neural substrates of LI as well as on the effects of APDs on this phenomenon with an attempt to interpret and integrate these data within the framework of the switching model of LI; to show that there are two distinct LI models, disrupted and abnormally persistent LI; to relate these findings to the clinical condition.

RESULTS

The nucleus accumbens (NAC) and its DA innervation form a crucial component of the neural circuitry of LI, and are involved at the conditioning stage. There is a clear functional differentiation between the NAC shell and core subregions whereby damage to the shell disrupts LI and damage to the core renders LI abnormally persistent under conditions that disrupt LI in normal rats. The effects of shell and core lesions parallel those produced by lesions to the major sources of input to the NAC: entorhinal cortex lesion, like shell lesion, disrupts LI, whereas hippocampal lesion, like core lesion, produces persistent LI with changes in context, and basolateral amygdala (BLA) lesion, like core lesion, produces persistent LI with extended conditioning. Systemically induced blockade of glutamatergic as well as DA transmission produce persistent LI via effects exerted at the conditioning stage, whereas enhancement of DA transmission disrupts LI via effects at the conditioning stage. Serotonergic manipulations can disrupt or potentiate LI via effects at the pre-exposure stage. Both typical and atypical APDs potentiate LI via effects at conditioning whereas atypical APDs in addition disrupt LI via effects at pre-exposure. Schizophrenia patients can exhibit disrupted or normal LI as a function of the state of the disorder (acute versus chronic), as well as persistent LI.

CONCLUSIONS

Different drug and lesion manipulations produce two poles of abnormality in LI, namely, disrupted LI under conditions which lead to LI in normal rats, and abnormally persistent LI under conditions which disrupt it in normal rats. Disrupted and persistent LI are differentially responsive to APDs, with the former reversed by both typical and atypical APDs and the latter selectively reversed by atypical APDs. It is suggested that this "two-headed LI model" mimics two extremes of deficient cognitive switching seen in schizophrenia, excessive and retarded switching between associations, mediated by dysfunction of different brain circuitries, and can serve to model positive symptoms of schizophrenia and typical antipsychotic action, as well as negative symptoms of schizophrenia and atypical antipsychotic action.

Arbeitsgedächtnis und Kontextinformationen mit dem Turm von Hanoi

Zusammenfassung: Gegenstand der Arbeit ist eine neuropsychologische Theorie für den Turm von Hanoi (TvH). Die Theorie basiert auf den theoretischen Konzepten des Arbeitsgedächtnisses und der Nutzung von Kontextinformationen. Die Verhaltensstörung (i. S. von Regelverstößen), die nach Frontalhirnläsion der linken Hemisphäre auftritt, kann als fehlerhafte Reaktionsauswahl aufgrund der läsionsbedingten fehlenden Berücksichtigung von Kontextinformation im Arbeitsgedächtnis definiert werden. Im empirischen Teil werden 146 hirngeschädigte Patienten und 150 gesunde Kontrollen mit dem TvH und einem Gedächtnistest (Tempoleistung und Merkfähigkeit Erwachsener; TME) untersucht. Neben vergleichbaren Zügen im TvH weisen die Hirngeschädigten verlängerte Lösungszeiten und vermehrt Regelverstöße auf. Die Regelverstöße korrelieren höher mit den Leistungen der visuellen Merkfähigkeit im TME als mit den Problemlöseindikatoren des TvH. Die Patienten mit unilateralen oder bilateralen frontalen Läsionen unterscheiden sich nicht in den Lösungszeiten gegenüber den Patienten mit multiplen oder unilateral, posterioren Läsionen. Dagegen weisen die Patienten mit links-frontalen, bilateral frontalen und multiplen Läsionen gehäuft Regelverstöße auf.

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

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

Noradrenergic modulation of cognitive flexibility in problem solving

Stress causes impaired performance on tests of creativity. Drugs that block beta-adrenergic receptors improve test performance in patients with test anxiety. Furthermore, catecholamine precursors (L-DOPA) reduce the flexibility of semantic networks. Our study investigated the effect of noradrenergic system modulation on cognitive flexibility in problem solving. Eighteen normal subjects undertook three problem solving tasks (number series, shape manipulation and anagrams) 45 min after propranolol, placebo and ephedrine. On the task that appeared to rely most heavily on cognitive flexibility (anagrams), subjects who were most able to solve these problems demonstrated significantly shorter solution times (logarithmic scores) after propranolol than after ephedrine. This suggested that the noradrenergic system exerts a modulatory effect on cognitive flexibility in problem solving.

Inherited cerebellar diseases

This chapter analyzes the neuropsychological deficits in inherited cerebellar diseases and compares their symptomatology with animal models in which the exact anatomical localization of degeneration is known and limited to the cerebellum. Both animal and human data suggest that cerebellar cortical atrophy affects functions of the frontal lobe system. Olivopontocerebellar atrophy is genetically and clinically in homogeneous. The dementia syndrome that occurs in a proportion of patients does not seem to be linked with cerebellar dysfunction. Patients suffering from Friedreich's disease have been described as exhibiting cognitive slowing and deficits in spatial tasks. Because other structures are more prominently involved than the cerebellum in this disease, other pathoanatomical correlates may explain the symptomatology.

Outlining a brain model of mental imaging abilities

This paper outlines a brain model of mental imaging abilities by reviewing neuropsychological evidence of the association and dissociation between mental imaging processes and known perceptual mechanisms; differentiating between visual-mode and auditory-mode thought systems; pointing to brain arousal systems involved in waking and dream imaging; and exploring pre-frontal involvement in deliberate imaging and cognitive state monitoring. In the process, the paper develops an emerging distinction between objective-imagery and subjective-imagery abilities. It ends by suggesting possible brain models for in-born and clinical loss of subjective imaging abilities.

PET imaging of maze processing

Covered maze traversal models nonverbal planning, involving sequential execution of moves using learned spatial maps. To determine the neural substrate involved in maze processing, eleven adults underwent [H(2)15O]-PET while performing motor control, following the computer; visual control, choosing the wall with more dead-ends; uncovered maze, traversing fully visible mazes; covered maze, traversing mazes only locally visible. Maze processing lateralizes to the right hemisphere: uncovered maze versus controls revealed area 23 and 29 activation; covered maze versus controls activated areas 8, 10 and 19. The extrastriate region may store path information, evoked by prefrontal areas for spatial planning and navigation.

Effects of focal brain lesions on visual problem-solving

In this study, the relative contributions of different brain regions to visual problem-solving were explored using a new test of divergent thinking. Seventy-three patients with focal brain lesions and 20 normal control subjects performed a set of matchstick problems, similar to those described by Guilford [15] as a measure of adaptive flexibility. For each problem, subjects were to demonstrate as many ways as possible of removing a particular number of sticks from a two-dimensional geometric design to achieve a specified resultant shape. Patients with left temporal-occipital, right temporal-occipital, or left frontal lesions displayed no significant difficulty. Evidence of general deficiencies in the ability to manipulate this visual material was seen in patients with parietal and/or central-area lesions (right worse than left). In contrast, patients with right frontal-lobe damage demonstrated a selective impairment in the ability to shift strategy. The results confirm the importance of the right suprasylvian region in the ability to process and act on visual information. They also provide evidence of the specific role played by the right frontal lobe, and particularly the ventral region, in permitting a flexible approach to visual problem-solving.

Fetal alcohol exposure alters the induction of immediate early gene mRNA in the rat prefrontal cortex after an alternation task

The present study examined fetal alcohol effects (FAE) on the induction of the immediate early genes (IEGs) c-fos, jun B, c-jun, and zif268 mRNAs in the prefrontal cortex, hippocampus, and other brain regions after testing in an alternation task. Subjects were female offspring of Sprague-Dawley rats fed either a 35% ethanol-derived calorie diet, pair-fed with sucrose, or control-fed with laboratory chow during the last week of gestation. At 75-85 days of age, rats were food-deprived and trained in a t-maze for food reward. Then rats were tested at 5-sec, 30-sec, or 60-sec delays on each of 6 days. On the day of killing, a subset of rats was tested at the 60-sec delay for 12 trials and killed 30 min after testing. The remaining animals were killed from their home cage and acted as controls. Expression of the four IEG mRNAs was examined in the brains of these animals using in situ hybridization. FAE rats showed a memory deficit at the 60-sec delay (p < 0.05), but not at the 0-sec or 30-sec delays. Testing in the alternation task induced a significant elevation of c-fos, c-jun, jun B, and zif268 mRNA expression in the prefrontal cortex, hippocampal subfields CA1 and CA3, and several cortical areas. However, FAE rats showed a significantly smaller elevation of both c-fos and jun B mRNA levels in the orbital, prelimbic, and anterior cingulate regions of the prefrontal cortex (p < 0.05). FAE animals also showed a lower expression of jun B mRNA in the caudate nucleus. Significant correlations between the mean performance at the 60-sec delay and mRNA expression of c-fos, jun B, and zif268 in the prefrontal cortical regions (p < 0.05) were observed. These findings suggest that fetal alcohol exposure produces changes in the adult prefrontal cortex that may contribute to the behavioral deficit in the alternation task.