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Archives of Clinical Neuropsychology20 (2005) 771783

Neuropsychological functioning of dementiapatients with psychosis

Mary W. Hopkinsa, David J. Libonb,a Department of Psychology, Manhattanville College, Purchase, New York, USA

b Center for Aging, University of Medicine and Dentistry of New JerseySchool of Osteopathic Medicine,Suite 1800, 42 East Laurel Road, Stratford, NJ 08084, USA

Accepted 9 April 2005

Abstract

The current research sought to test the hypothesis that psychotic symptoms in patients with de-mentia might be due to relatively greater executive control and visuoperceptual deficits. Twenty-fourdementia patients with psychosis and 24 outpatients without psychosis diagnosed with either proba-ble Alzheimers disease (AD) or possible/probable Ischemic Vascular Dementia (IVD) were studied.Groups did not differ with respect to age, education, severity of dementia, or depression. Presenceand severity of psychosis was measured with a modification of the Neuropsychiatric Inventory (NPI;Cummings, J. L., Mega, M., Gray, K., Rosenberg-Thompson, S., Carusi, D. A., & Gorbein, J. (1994).The neuropsychiatric inventory: Comprehensive assessment of psychopathology in dementia.Neurol-ogy, 44, 23082314). Between-group and regression analyses found a consistent relationship such thatpatients with psychosis obtained low scores on the Boston Revision Wechsler Memory Scale-MentalControl subtest (WMS-MC subtest), a test of executive control. On some analyses patients with psy-chosis also made more perceptual errors on tests of naming and obtained higher scores on tests ofdelayed recognition memory. However, the relationship between severity of psychosis and performanceon visuoperceptual and memory measures was considerably less robust. These data suggest a strongrelationship between severity of psychosis and poor performance on executive control. Less evidencewas obtained to support our contention that psychotic symptoms in dementia may arise from an in-

Material presented in this paper is based, in part, on work performed by Mary W. Hopkins, in fulfillment of the dissertationrequirement for the Doctor of Education degree at Argosy University, Sarasota, FL.

Corresponding author.E-mail address: [email protected] (D.J. Libon).

0887-6177/$ see front matter 2005 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.acn.2005.04.011

772 M.W. Hopkins, D.J. Libon / Archives of Clinical Neuropsychology 20 (2005) 771783

teraction of neuropsychological deficits involving greater impairment in executive and visuoperceptualfunctioning. 2005 National Academy of Neuropsychology. Published by Elsevier Ltd. All rights reserved.

Keywords: Dementia; Psychosis; Delusions; Paraphrenia; Subcortical dementia; Alzheimers disease; Vasculardementia

1. Introduction

Cognitive dysfunction is generally considered the defining feature of dementia. Nonetheless,the presence of non-cognitive symptoms, such as hallucinations and delusions, is common.For example, incidence and prevalence rates for delusions and hallucinations in dementiarange from 1% to 46% and 3% to 73%, respectively (Ballard & Walker, 1999; Wragg &Jeste, 1989). Greater neuropsychological and functional impairment have been reported indementia patients who experience psychotic symptoms (Doody, Massman, Mahurin, & Law,1995; Drevets & Rubin, 1989; Lopez, Wisneiski, Becker, Boller, & DeKosky, 1999; Sternet al., 1994). However, less certain is the nature of the relationship between neuropsychologicalfunctioning and psychotic symptoms.

A number of researchers have presented evidence that impairment in specific cognitivefunctions is associated with psychotic symptoms in dementia patients, either singly or in somecombination. In this regard, associations have been reported between psychotic symptoms andimpaired performance on tests of executive control (Paulsen et al., 2000), receptive language(Lopez et al., 1991) and perceptual impairments (Fleminger & Burns, 1993) in dementedpatients. Research demonstrating an association between psychotic symptoms and lesions ofthe right hemisphere, basal ganglia, and temporal lobes has led some researchers to postulatethat psychotic symptoms may be mediated by executive system misinterpretation of distortedor inaccurate sensory stimuli (Cloud, Carew, Rothenberg, Malloy, & Libon, 1996; Fleminger,1992, 1994; Mega et al., 2000).

Alternatively, Cummings and colleagues (Flynn, Cummings, & Gorbein, 1991; White &Cummings, 1996) have argued that psychosis and cognition dysfunction arise from indepen-dent mechanisms and that psychotic symptoms may reflect underlying limbic system and basalganglia dysfunction associated with neurotransmitter deficiencies. The failure of some studiesto find any relationship between delusions and other psychotic symptoms and specific neu-ropsychological impairments supports this point of view (Flynn et al., 1991; Migliorelli et al.,1995).

In the current study dementia patients with and without psychotic symptoms were admin-istered tests that assess executive control, visuoperceptual, language, and memory functions.The aim of this study was to examine the hypothesis that psychotic symptoms in dementia areassociated with an inability of executive control functions to regulate or put into context com-plex visuoperceptual stimuli. This hypothesis is derived from the work ofCloud et al. (1996)andFleminger (1992, 1994)cited above. Therefore, our aim was to test the prediction thatdemented patients with psychosis would obtain particularly low scores on executive control,and, perhaps, visuoperceptual tests as compared to a non-psychotic cohort.

M.W. Hopkins, D.J. Libon / Archives of Clinical Neuropsychology 20 (2005) 771783 773

2. Methods

2.1. Participants

Participants for this study were serial referrals to an outpatient dementia evaluation programat the Crozer-Chester Medical Centers Alexander Silberman Geriatric Assessment ProgramCenter. All patients were examined by a social worker, geriatrician, neurologist, psychiatrist,and a neuropsychologist. MRI and laboratory studies were obtained for all patients. Patientswere diagnosed at an inter-disciplinary team conference. Following full diagnostic and neu-ropsychological assessment, 24 patients diagnosed with dementia who also presented withpsychotic symptoms were identified. Within the psychotic group, 13 patients were diagnosedwith probable AD using NINCDS-ADRDA criteria (McKhann et al., 1984) and 11 patientswere diagnosed with possible/probable Ischemic Vascular Dementia (Chui et al., 1992). Forcomparative purposes, 24 demented patients without psychosis were also studied (AD = 14;IVD = 10). No patient with AD presented with either a cortical or subcortical CVA. No patientswere taking psychoactive medication.

As shown inTable 1, there were no between-group differences in age, education, the severityof dementia as assessed by the Mini-Mental Status Examination (MMSE;Folstein, Folstein,& McHugh, 1975), or depression as assessed with the Geriatric Depression Scale (Yeasavage,1986). Participants were excluded if there was any history of head injury, substance abuse,major psychiatric disorders (including major depression), epilepsy, B12 deficiency, folatethyroid deficiency, or Parkinsons disease. These data were gathered from medical records anda knowledgeable family member.

2.2. Neuropsychological assessment

The following domains of neuropsychological functioning were assessed.Executive controlwas assessed with the Boston Revision of the Wechsler Memory Scale-

Mental Control subtest (WMS-MC;Lamar, Price, Davis, Kaplan, & Libon, 2002). The BostonRevision of the WMS-MC subtest is an extension of the standard WMS-MC subtest and wascreated to enhance its ability to detect cases of mild or subtle cognitive impairment. The stan-dard WMS-MC subtest includes three tasks: counting from 20 to 1, reciting the alphabet, andadding serial 3s (Wechsler, 1945). The Boston Revision of the WMS-MC subtest expands theWMS-MC subtest by including four additional tasks: reciting the months of the year forwardand backward, an alphabet rhyming task, which requires patients to provide all letters that

Table 1Demographic and medical variablesmeans (standard deviations)

Psychosis present Psychosis absent

Age 78.37 (6.63) 79.75 (7.07)Education 11.33 (2.82) 11.54 (2.80)Mini Mental State Exam 22.17 (4.14) 20.50 (3.22)Geriatric Depression Scale 7.42 (4.06) 6.08 (3.19)


rhyme with the word key, and an alphabet visualization task, which requires patients to pro-vide all block printed letters that contain curved lines. Participants are allowed to work as longas necessary on these tasks provided they are working meaningfully. The dependent variablederived from this test is an Accuracy Index (AcI) based on the three non-automatized tasks(i.e. months backward, alphabet rhyming, alphabet visualization). This accuracy index is basedon the following algorithm: AcI = [1 (false positive + misses/# possible correct)]100. Apercentage score ranging from 0 to 100 is derived from this algorithm. Using this system,a score of 100% indicates that the patient correctly identified all targets and made no falsepositive responses (i.e. errors) or misses. A composite score assessing performance on thenon-automatized mental control tasks is calculated by averaging the AcI for each of thesethree tasks for each patient. Similar tests have been shown to activate the prefrontal cortex(Paulesu, Frith, & Frackowiak, 1993).

Executive control was also assessed with a test of word list generation (FAS;Spreen &Strauss, 1998). Participants were given 60s to generate as many words as possible beginningwith a specified letter excluding proper nouns or the same word with a different suffix (e.g. findand finding). The dependent variable is the number of correct responses summed across eachletter. Imaging studies have shown that this task activates the dorsolateral prefrontal cortex inolder adults (Gourovitch et al., 2000).

Additionally, executive functioning was assessed by asking patients to draw the face ofa clock with the hands set for ten after eleven in both a command and copy condition(Goodglass & Kaplan, 1983). Following procedures described byLibon, Malamut, Swenson,Sands, and Cloud (1996)three types of errors were tallied: errors related to graphomotor im-pairment, errors in hand/number placement, and errors related to executive control impairment.Each error received a score of either 1 (i.e. present) or 0 (i.e. absent). The dependent variablewas total number of errors. Recently,Cosentino, Jefferson, Kaplan, and Libon (2004)haveshown that total clock drawing errors is linked to differentially poor performance on executivecontrol tests as compared to other domains of cognitive functioning.

Language/semantic functioningwas assessed with the Boston Naming Test (BNT;Kaplan,Goodglass, & Weintraub, 1983). The dependent variable derived from the BNT is the numberof correct responses. Language/Semantic functioning was also assessed with the animal wordlist generation task (Carew, Lamar, Cloud, Grossman, & Libon, 1997). Participants were given60 s to generate responses. The dependent variable is the total Association Index (AI). The AI isa special scoring technique that measures the semantic integrity between successive responses.A high score on this measure is believed to reflect generally intact semantic memory stores.Complete details regarding AI derivation and scoring can be found inCarew et al. (1997).Differentially worse performance on the animal word list generation task has been associatedwith the temporal lobe pathology associated with Alzheimers disease (Sailor, Antoine, Diaz,Kuslansky, & Kruger, 2004).

Visuoperceptual functioningwas assessed by tallying perceptual and whole/part errors fromthe Boston Naming Test (Kaplan et al., 1983). Perceptual errors were scored when patientsresponses suggested that they were not identifying the line drawing accurately. For example, thepatient may refer to the picture of the harmonica as a double-decker bus or a box where youkeep your nuts and bolts. Whole/part errors were scored when patients correctly identifiedonly one feature or part of the presented item. For example, a whole/part error was scored


when the patient was presented with a picture of a dart and responded, its a feather. Priorresearch suggests that these types of errors are linked to perceptual deficits sometime linkedto right hemisphere dysfunction, rather than to linguistic deficits (Nicholas, Obler, Albert, &Goodglass, 1983).

Memory and learningwas assessed with the 9-word version of the California Verbal Learn-ing Test (CVLT; Libon et al., 1996b). The construction and administration of the 9-wordCVLT is identical to the standard 16-word CVLT (Delis, Kramer, Kaplan, & Ober, 1987).For the present research three dependent variables were analyzed: the List Aimmediate freerecall, the recognition discriminability index, and the percent of cued recall intrusions.Libonet al. (1998)have shown that greater parahippocampal volume is linked to higher CVLT-9recognition discriminability test scores.

2.3. Assessment of psychosis

The severity of psychotic symptoms was assessed with a modified version of the delusionand hallucination indices of the Neuropsychiatric Inventory of Cummings (NPI;Cummingset al., 1994; Tables 2a and 2b).

The Neuropsychiatric Inventory-Modified (NPI-M) consists of two parts. Part I is a self-administered questionnaire completed by the patients spouse and/or family. This was takenfrom the standard NPI questionnaire and was used to identify psychotic behaviors. Part 2 ofthe NPI-M consists of a structured interview completed by the examiner with family members.Psychotic symptoms identified on Part 1 of the NPI-M were rated on the five dimensions listedbelow modeled afterGarrety and Helmsley, (1987)using a 4-point Likert scale (Table 2a).Table 2b lists descriptive statistics for this information.

Table 2aAssessment of psychotic symptoms with the Neuropsychiatric Inventory-Modified

(I.) Frequency ofoccurrence

13 times/month 47 times/month 812 times/month >12 times/month

1 2 3 4

(II.) Resistance toconfrontation

100% of time 50% of time


Table 2bMeans and standard deviations for psychosis subscales

Scale 1(frequency)

Scale 2(confrontation)

Scale 3(belief)

Scale 4(distress)

Scale 5(chronicity)

Total

Mean 6.25 5.00 5.75 4.54 4.91 26.45S.D. 5.05 3.38 4.28 3.61 5.53 20.18Range 15.00 13.00 14.00 12.00 18.00 66.00

(1) Frequencythe number of occurrences of psychotic symptoms during the last month.(2) Resistance to confrontationthe degree to which the patient can be persuaded that their

psychotic symptoms are not real.(3) Convictionthe degree the patient believes that their psychotic symptoms have some

basis in reality.(4) Distressthe degree of emotional upset caused by psychotic symptoms.(5) Chronicitythe percent of time over the entire course of the patients dementia that

psychotic symptoms have been present.

The dependent variable derived from the NPI-M was a total psychosis scale calculated bytallying the scores from all five dimensions listed above.Table 2b lists the mean and standarddeviation for each of the NPI-M subscales. Higher values indicate more severe psychosis.On average patients with psychosis exhibited 1.3 (S.D. = 3.4) psychotic symptoms. The mostcommon symptoms reported involved delusions of theft, jealously, and the report of seeingor hearing strangers living in the patients homes. No participant exhibited a paraphrenia orthought disorder.

3. Results

3.1. Psychotic versus non-psychotic comparisons

The effect of psychosis on neuropsychological functioning was assessed with a series ofmultivariate analyses of variance (MANOVAs) for each domain of neuropsychological func-tioning. In these analyses dementia patients with psychosis versus dementia patients withoutpsychosis was the independent variable. The scores on neuropsychological tests were thedependent variables (Table 3). Even though there was no between-group difference on theMMSE, simple correlations indicated borderline significance between the MMSE and BostonNaming Test (r = .353,P< .045) and CVLT recognition discriminability test score (r = .374,P< .036). Significant correlations were noted between the MMSE and the Wechsler MemoryScale-Mental Control subtest (r = .436,P< .016) and the CVLT total immediate recall-List A(r = .508,P< .001). Therefore, in all of the analyses described below the MMSE was co-varied.

The MANOVA assessing for between-group differences in executive functioning was sig-nificant (F [3, 43] = 6.09,P< .002). Follow-up ANOVAs indicated that compared to the non-psychotic patients, psychotic patients obtained lower scores on the WMC-MC Subtest (F [1,


Table 3Neuropsychological Testsmeans (standard deviations)

Group Psychosis present Psychosis absent

Executive functioningWMS-MC (AcI)a 50.04 (22.95) 66.95 (12.86)**

COWA-FAS Testb 15.42 (7.60) 16.63 (5.66)Clock Drawing Test 6.20 (2.48) 6.54 (2.96)

LanguageBNTTotal Correctc 40.29 (9.10) 29.17 (10.25)***

Animal WLGNo. of Responsesd 8.50 (3.01) 7.79 (2.41)Animal WLGTotal AIe 3.37 (.8754) 3.35 (.5391)

Visuoperceptual functioningBNTPerceptual Errorsf 2.42 (2.54) 2.38 (2.12)BNTWhole/Part Errorsg .37 (.58) .38 (.65)

Memory and learningCVLTFree Recallh 21.75 (7.18) 17.96 (6.82)CVLTPercent CuedRecall Intrusionsi 27.81 (22.81) 31.89 (23.10)CVLTRecognitionDiscriminabilityj 84.04 (9.84) 76.88 (9.23)

a Wechsler Memory Scale-Mental Control subtest-Accuracy Index.b Controlled Oral Word Association (FAS).c Boston Naming Test.d animal Word List Generation TestNumber of Responses Index.e animal Word List Generation TestTotal Association Index.f Boston Naming TestPerceptual Errors Index.g Boston Naming TestWhole/Part Errors Index.h California Verbal Learning TestList A Free Recall Index.i California Verbal Learning TestPercent Cued Recall Intrusions Index.j California Verbal Learning TestRecognition Discriminability Index. P< .05. P< .005. P< .001.

45] = 15.97,P< .001; Table 2). No significant differences between the psychotic and non-psychotic groups were found on either tests of letter fluency (FAS) or the Clock DrawingTest.

The MANOVA examining for the effect of group on tests of language was also significant(F [3, 43] = 4.17,P< .011). AsTable 3shows, follow-up comparisons indicated that dementiapatients with psychosis correctly named more items on the Boston Naming Test than did non-psychotic demented patients (F [1, 45] = 12.55,P< .001). None of the other between-groupcomparisons were significant. Regarding visuoperceptual errors from the Boston Naming Test,the multivariate effect for group was not significant (Table 3).

Within the domain of memory, differences between psychotic and non-psychotic groupsreached only borderline significance (F [3, 43] = 2.58,P< .182), indicating less impairment inmemory among the psychotic group. AsTable 3shows, follow-up ANOVAs indicated that on


Table 4Neuropsychological Testsmeans (standard deviations)

Group Low psychosis High psychosis

Executive functioningWMS-MC (AcI)a 60.75 (23.50) 39.33 (17.29)

COWA-FAS Testb 19.00 (7.02) 11.83 (6.59)

Clock Drawing Test 5.41 (3.02) 7.00 (1.53)

LanguageBNTTotal Correctc 40.25 (11.68) 40.33 (6.07)Animal WLGNo. of Responsesd 9.17 (3.01) 7.83 (2.98)Animal WLGTotal AIe 3.34 (.75) 3.40 (1.01)

Visuoperceptual functioningBNTPerceptual Errorsf 1.00 (1.28) 3.83 (2.72)**

BNTWhole/Part Errorsg .17 (.39) .58 (.67)

Memory and learningCVLTFree Recallh 19.92 (7.69) 23.58 (6.42)CVLTPercent CuedRecall Intrusionsi 24.28 (25.24) 31.35 (20.58)CVLTRecognitionDiscriminabilityj 86.33 (8.52) 81.75 (10.87)

a Boston Revision of the Wechsler Memory Scale-Mental Control subtestAccuracy Index.b Controlled Oral Word Association (FAS).c Boston Naming TestTotal Correct.d animal Word List Generation TestNumber of Responses Index.e animal Word List Generation TestTotal Association Index.f Boston Naming TestPerceptual Errors Index.g Boston Naming TestWhole/Part Errors Index.h California Verbal Learning TestList A Free Recall Index.i California Verbal Learning TestPercent Cued Recall Intrusions Index.j California Verbal Learning TestRecognition Discriminability Index. P< .05. P< .01.

tests of delayed recognition, demented patients with psychosis obtained a higher score thannon-psychotic demented patients (CVLT Recognition Discriminability index (F [1, 45] = 4.64,P< .037).

3.2. Low psychosis versus high psychosis comparisons

To evaluate the effect of severity or level of psychosis on cognitive functioning, a second setof MANOVAs was performed after a median split divided patients with psychosis into groupswith a comparatively low degree versus a high degree of psychosis (i.e. low psychosis versushigh psychosis groups). The multivariate effect of group on tests of executive functioning wasborderline (F [3, 19] = 2.86,P< .064). AsTable 4shows, follow-up ANOVAs indicated patientswith a high degree of psychosis continued to obtain lower scores on the WMS-MC subtest (F[1, 21] = 7.02,P< .015). There was a borderline effect such that patients with a high degree ofpsychosis tended to generate fewer responses on tests of letter fluency (FAS) (F [1, 21] = 6.25,


P< .021). The MANOVA examining for between-group differences for visuoperceptual errorsfrom the BNT was now significant (F [2, 20] = 5.76,P< .011). Follow-up ANOVAs indicatedthat the high psychosis group made significantly more perceptual errors on the BNT than thelow psychosis group (F [1, 21] = 10.16,P< .004) and there was a trend for patients in the highpsychosis group to make more whole/part errors (F [1, 21] = 3.23,P< .086). The MANOVAexamining for the effect of high versus low psychosis did not result in significant differenceson either any of the CVLT or language measures.

As an additional test of our prediction that dementia patients with psychosis present withdifferential executive control and visuoperceptual impairment, a stepwise regression analysiswas conducted with the total psychosis score as the dependent variable and the WMS-MCsubtest, total score on the BNT, total perceptual and whole/part errors on the BNT, and theCVLT-recognition discriminability as the independent variables. To control for overall levelof dementia the score on the MMSE was entered first. The results of this analysis indicatethat after the MMSE was entered (r = .284,R2 = .081) performance on the WMS-MC washighly significant (r = .688,R2 = .474), accounting for almost 50% of the variance for the totalpsychosis measure. None of the other three variables entered into the analysis.

4. Discussion

The question of why some, but not all, dementia patients develop psychosis is not well un-derstood. This was the impetus for this investigation. To explore this issue, we compared thepattern of neuropsychological functioning in dementia patients with and without psychosis.Our primary hypothesis was that when compared to demented patients without psychosis,demented patients with psychosis would exhibit a distinct pattern of neuropsychological func-tioning characterized by greater executive and visuoperceptual impairment. The data onlypartially confirmed our underlying prediction, i.e. psychotic patients did produce lower scoreson some tests of executive control in comparison to non-psychotic patients. This was foundwhen the psychotic group was compared to the non-psychotic group, when patients with lesssevere levels of psychosis were compared to patients with greater levels of psychosis, andin step-wise regression where performance on the Boston Revision of the Wechsler Mem-ory Scale-Mental Control subtest accounted for almost 50% of the variance when severityof psychosis was the dependent variable. This study provided additional confirmation of theimportance of executive dysfunction in psychosis in dementia. Our data are, therefore, con-sistent with numerous prior studies linking psychosis in dementia and related disorders withmetabolic and perfusion abnormalities of the frontal lobes (Binetti et al., 1995; Cloud et al.,1996; Mega et al., 2000; Sultzer et al., 1995) and/or with executive dysfunction (Chen, Sultzer,Hinkin, Mahler, & Cummings, 1998; Jeste, Wragg, Salmon, Harris, & Thal, 1992; Megaet al., 2000; Paulsen et al., 2000).

The question of precisely how executive dysfunction contributes to the generation of psy-chotic phenomenon is complex. Executive function is a relatively imprecise construct thatencompasses multiple higher-order cognitive abilities. In the present research tests that assessa wide range of executive control abilities were used. In previous research we have suggestedthat the Boston Revision of the Wechsler Memory Scale-Mental Control and tests of letter flu-


ency provide a measure of working memory whereas other tests such as clock drawing providea measure of perseveration (Libon, Price, Garrett, Giovannetti, 2004). Only our tests of workingmemory were related to severity of psychosis. In psychosis, executive defects have frequentlybeen depicted as causing an erosion of reality testing and self-monitoring capacities whichdisables the individuals capacity to integrate, evaluate, and interpret experience; placing theindividuals ability to accurately assess the veracity of what is perceived and to contextualizeexperience in jeopardy (Cloud et al., 1996; Fleminger, 1992, 1993, 1994). It is possible thatworking memory may play a role in this process. Does executive control impairment cause orgive rise to psychotic symptoms or vice versa? The data presented above is not really able toprovide a comprehensive answer to this question. Nonetheless, we speculate that the aetiologyof psychotic behavior in dementia involves a complex interaction of derailed capacity of thefrontal lobes to regulate executive control functions including working memory (Luria, 1980)in combination with other neural structures such as the posterior cortex and limbic structures.Clearly, this is an area for additional research.

That visuoperceptual deficits would also be associated with the generation of psychoticsymptoms in dementia is consistent with prior data implicating impaired perceptual mecha-nisms (Burns, Jacoby, & Levy, 1990b; Farber et al., 2000). However, support for this predictionin the current research was weak. For example, patients with higher levels of psychosis didproduce more perceptual errors on the BNT than patients with low levels of psychosis anddemonstrated a trend toward more BNT whole/part errors suggesting that greater perceptualsystem deficits contribute to more severe symptoms in affected individuals. However, contraryto expectations, comparison of psychotic and non-psychotic patients as a whole did not revealany group differences in visuoperceptual functioning (i.e. BNTperceptual and whole/partindices). Also, perceptual errors from the BNT did not enter into the step-wise regressionanalysis described above. This inconsistency, may, in part, have been due to the means bywhich visuoperceptual deficits were measured. The existence of separate neurocognitive sys-tems involved in object location and object recognition (Farah, 2003) is well established. Anassessment of how these types of perceptual functions interact with derailed executive controlfunctioning might yield more information about the nature of psychotic symptoms in dementia.There may also be an association between subcortical pathology, which typified our patientswith IVD and the production of psychotic symptoms. For example, psychotic symptoms arewell known to occur in other groups of patients with subcortical dementia such as Parkinsonsdisease (PD;Wint, Okun, & Fernandez, 2004). Newer research suggests that psychosis in dis-orders such as PD is associated with multiple neurochemical and neuropsychological factors.The similarities and differences regarding psychotic symptoms between patient groups withdifferent types of subcortical pathology could yield new insights into this vexing problem.

More severe memory impairment has also been invoked as a possible contributory mech-anism in psychosis. For example,Mendez (1992)has argued that psychotic symptoms arisefrom a weakened sense of familiarity or a disparity between new perceptions and past mem-ories. However, contrary to these findings, data from the present study indicates that bothlanguage and memory might be less impaired in psychotic patients than in non-psychotic pa-tients. These unanticipated findings could suggest that psychosis does not arise from deficitsin specific domains only, but rather requires better preservation of some capacities (viz., betterlexical retrieval and semantic memory stores).


Some authors have attempted to explain psychotic formation from a neuropsychologicalperspective. In this regard bothCloud et al. (1996)andFleminger (1994)have argued that faultyprocessing related to the generation and interpretation of sensory impressions underlies delu-sion formation. Moreover,Cloud et al. (1996)have argued that enhanced memory capacities areessential to, and in fact, increase the likelihood of, delusion formation. From this perspective,psychosis is dependent upon the individuals ability to rehearse and store incorrect hypothesesor judgments that are generated when ambiguous perceptual stimuli are misinterpreted due to areality-monitoring deficit (Cloud et al., 1996, p. 151). Thus, according toCloud et al. (1996),delusions represent long term memory traces (p. 151) of erroneous perceptions and infer-ences. Our data do not provide direct support for this model. Nonetheless, such psychologicalexplanations for the aetiology of psychosis in dementia merit further research.

The present research is not without some limitations. For example, this study investigated,without differentiation, patients who fell into one of two broad diagnostic categories, ADand IVD. The small sample available for study made further division into separate subgroupsunfeasible (i.e. would have reduced power to an unacceptably low level). Failure to assesspossible differences in neuropsychological performance between AD and IVD patients isa methodological limitation of the present research that may have masked real differencesbetween AD and IVD patients. Therefore, future research involving a larger sample withwell-characterized subgroups of dementia patients is recommended.

Various psychotic symptoms may have different clinical and neuropathological correlates;therefore our inability to differentiate different types of psychotic symptoms may have limitedthe conclusions that can be drawn from this research. Despite these limitations, our findingsoffer preliminary evidence that distinct patterns of neuropsychological impairment might beassociated with psychosis in dementia.

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Neuropsychological functioning of dementia patients with psychosisIntroductionMethodsParticipantsNeuropsychological assessmentAssessment of psychosis

ResultsPsychotic versus non-psychotic comparisonsLow psychosis versus high psychosis comparisons

DiscussionReferences

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