Neuropsychological aspects of Parkinson's disease

The neuropsychological effects of Parkinson's disease have gained wide recognition in recent literature. Effects have been documented in almost all areas of cognitive functioning, including general intellectual functioning, visual-spatial functioning, executive functions, attention and memory functions, language functions, and affective processes. Visual-spatial functions, memory functions, and executive functions have received particular interest. This review of the literature is an attempt to tie together the large number of studies in these cognitive areas and to present a suggestion for a comprehensive neuropsychological battery tailored to the patient with Parkinson's disease. Throughout the review, factors relevant to Parkinson's disease, e.g., dementia, motor symptoms, and hemiparkinsonism, are considered.     

Neuropsychological impairment in Parkinson's disease without dementia

Cognitive dysfunction in Parkinson's Disease (PD) has been consistently reported, but little is known about cognitive impairment in PD patients without dementia, and its association with clinical characteristics, neuropsychiatric disturbance and functional activities. Therefore, we evaluated 52 non-demented PD patients, 22 of them with mild cognitive impairment (PD-MCI) who were matched with 52 healthy controls. Our results confirm the existence of dysfunction in information processing speed, executive function, verbal memory and visuo-perceptual processing in PD. On the other hand, PD-MCI was associated with advanced age at the onset of PD, more neuropsychiatric symptoms, caregiver stress and functional problems. The study supports the hypothesis that specific neuropsychological impairments may act as modulators of functional impairment in PD, for instance slowness of information processing.     

Non-motor aspects of Parkinson's disease

Parkinson's disease is primarily considered to be a movement disorder and is defined by its motor signs. Yet, the behavioral manifestations of the disease are often more debilitating than its motor complications. This review will focus on the non-motor aspects of Parkinson's disease, including mood, psychosis, cognitive, sleep, fatigue, apathy, delirium, and repetitive disorders, that may occur. The phenomenology, pathology, and treatment of the behavioral symptoms of Parkinson's disease will be discussed.     

Neuropsychological outcome following unilateral stereotactic pallidotomy in intractable Parkinson's disease

Neuropsychological functioning was examined at baseline and 2- to 3-month follow-up in 40 subjects with advanced Parkinson's disease (PD) who underwent unilateral posteroventral pallidotomy. Most subjects demonstrated improved verbal learning, visual memory, confrontation naming, and figural fluency at follow-up. Right pallidotomy was associated with decreased cognitive flexibility and increased verbal fluency, whereas Left pallidotomy uniquely resulted in a decline in verbal fluency. Significant motor improvement was demonstrated in both groups. Pallidotomy appears to be an effective treatment for advanced PD, providing a significant improvement in motor functioning, while resulting in few deleterious neurocognitive changes in most cases.     

Productive syntax abilities in Huntington's and Parkinson's diseases

This study examined syntactic changes in the spoken discourse of patients with Huntington's (HD) or Parkinson's disease (PD) and explored possible relationships between their syntactic changes and concomitant cognitive and motoric symptoms. Patient and control groups participated in a conversational discourse activity and completed a battery of standardized speech and cognitive tests. The HD group used shorter and fewer grammatically complete utterances than their healthy, age-matched peers, whereas there were no significant syntactic differences between PD patients and their healthy, age-matched peers or between PD and HD patients. Productive syntax abilities in HD and PD were meaningfully related to both neuropsychological and motor speech changes. These findings indicate that patients with subcortical disease, at least those with HD, may present with language production deficits and that these deficits are most likely the product of not only motor speech limitations (i.e., dysarthria) but also underlying cognitive impairments.     

Neuropsychological outcome of GPi pallidotomy and GPi or STN deep brain stimulation in Parkinson's disease

This paper highlights the neuropsychological sequelae of posteroventral pallidotomy (PVP) and deep brain stimulation (DBS) of the subthalamic nucleus (STN) and the internal segment of the globus pallidus (GPi) at 3/6 months postoperatively. Results are based on our extensive experience with PVP and our preliminary observations with DBS. Patients with borderline cognitive or psychiatric functioning risk postoperative decompensation. Nonlateralizing attentional and hemisphere-specific impairments of frontostriatal cognitive functions followed unilateral PVP. "Frontal" behavioral dyscontrol was observed in approximately 25% of patients. Three cases of staged bilateral PVP suggest that premorbid factors may predict outcome, although lesion size and location are also critical. Older patients are at risk for significant cognitive and behavioral decline after bilateral STN DBS, while GPi DBS may be safer.     

Side of onset in Parkinson's disease and alterations in religiosity: novel behavioral phenotypes

Behavioral neurologists have long been interested in changes in religiosity following circumscribed brain lesions. Advances in neuroimaging and cognitive experimental techniques have been added to these classical lesion-correlational approaches in attempt to understand changes in religiosity due to brain damage. In this paper we assess processing dynamics of religious cognition in patients with Parkinson's disease (PD). We administered a four-condition story-based priming procedure, and then covertly probed for changes in religious belief. Story-based priming emphasized mortality salience, religious ritual, and beauty in nature (Aesthetic). In neurologically intact controls, religious belief-scores significantly increased following the Aesthetic prime condition. When comparing effects of right (RO) versus left onset (LO) in PD patients, a double-dissociation in religious belief-scores emerged based on prime condition. RO patients exhibited a significant increase in belief following the Aesthetic prime condition and LO patients significantly increased belief in the religious ritual prime condition. Results covaried with executive function measures. This suggests lateral cerebral specialization for ritual-based (left frontal) versus aesthetic-based (right frontal) religious cognition. Patient-centered individualized treatment plans should take religiosity into consideration as a complex disease-associated phenomenon connected to other clinical variables and health outcomes.     

Assessment of 'subcortical dementia' in patients with Huntington's disease, Parkinson's disease, multiple sclerosis and AIDS by a neuropsychological screening battery

Four diagnostic groups categorized as 'subcortical dementia' were studied using a neuropsychological screening battery. The specificity of the battery in disclosing characteristic patterns of impairment in subgroups within the category, and the correspondence between natural subgroups generated by an unsupervised statistical classification technique and the diagnostic labels were investigated. All cognitive affected subgroups demonstrated impairment on tests of sensomotor function, congnitive efficiency and/or memory, and were characterized in terms of severity of impairment as well as a progressive involvement of functional areas. The diagnostic groups were not evenly represented in all natural subgroups. Affected AIDS-patients seemed to resemble patients with Huntington's disease more than the other diagnostic groups. The screening battery could give a general characterization of the pattern of 'subcortical dementia' and different levels of impairment, but more specific process-oriented tasks are needed to contrast diagnostic groups within the concept of 'subcortical dementia'.     

Destination and source memory in Huntington's disease

Destination memory refers to the recall of the destination of previously relayed information, and source memory refers to the recollection of the origin of received information. We compared both memory systems in Huntington's disease (HD) participants. For this, HD participants and healthy adults had to put 12 items in a black or a white box (destination task), and to extract another 12 items from a blue or a red box (source task). Afterwards, they had to decide in which box each item had previously been deposited (destination memory), and from which box each item had previously been extracted (source memory). HD participants showed poorer source as well as destination recall performance than healthy adults in the proposed tasks. Correlation analysis showed that destination recall was significantly correlated with episodic recall in HD participants. Destination memory impairment in HD participants seems to be considerably influenced by their episodic memory performance.     

Lateralized effects of subthalamic nucleus stimulation on different aspects of speech in Parkinson's disease

In this report, we have analyzed the effects of left and right STN stimulation separately on different aspects of speech. Significant differences were found between left and right stimulation. It appears that selective left-sided stimulation has a profoundly negative effect on prosody, articulation and hence intelligibility. Right-sided stimulation does not display this side-effect. There is no significant difference in speech characteristics between bilateral stimulation on and off. We suggest that a balanced tuning of bilateral basal ganglia networks is necessary for speech, and that the left circuit is probably dominant.     

Neurolinguistic features of spontaneous language production dissociate three forms of neurodegenerative disease: Alzheimer's, Huntington's, and Parkinson's

An analysis of the temporal (prospective) form (silent and filled hesitations, repetitions, incomplete phrases, context-related comments, interjections), syntactic form, and lexical (retrospective) form (verbal deviations, open and closed class phrases) of spontaneous language production of early and middle stage Alzheimer's, Huntington's, and Parkinson's patients was made. Results showed that the language structure was disrupted in each disease, but in different ways. Temporal interruptions of varying types were frequent in the language of Alzheimer's and Huntington's Disease patients; only long-duration silent hesitations were frequent in Parkinson's language samples. Syntactic complexity was reduced in Huntington's Disease. Verbal paraphasias were found in both the language of Alzheimer's patients, as well as moderately advanced Huntington's patients. Closed class phrases were predominant in the language of Alzheimer's patients and Huntington's patients, and open class phrases in the language of Parkinson's patients. Taken together, the results suggest that (1) there is a unique neurolinguistic profile for spontaneous language production for each neurodegenerative disease, (2) pathology of the neostriatum disrupts syntactic organization, (3) adaptive strategies are used to cope with verbal and speech-motor difficulties, and (4) adaptive strategies fail to be effective with increasing disease severity.     

Associative encoding and retrieval in Alzheimer's and Huntington's disease

The associative encoding and retrieval abilities of patients with dementia of the Alzheimer type (DAT) and patients with Huntington's disease (HD) were investigated using an encoding specificity paradigm. When compared to age- and education-matched intact control subjects, both patient groups were severely (and equally) impaired on overall memory for word lists. However, the HD and DAT patients showed differential improvement in recall performance with the introduction of associated cues during stimulus presentation and recall. Although the HD patients, like intact subjects, were able to benefit from semantic retrieval cues (strong and weak) which were present during input, the performance of the patients with DAT improved only with the introduction of strong cues at output, regardless of whether the cues were present or absent during initial presentation. These findings suggest that patients with DAT failed to encode the semantic relationship between the to-be-recalled and cue words and simply generated free associations to the cue words during retrieval. Similarities between the performances of the patients with DAT and alcoholic Korsakoff patients are noted and discussed with regard to the neuropathological basis of the disorders.     

CT scan and neuropsychological correlates of Alzheimer's disease and Huntington's disease

"Cortical" and "subcortical" dementia syndromes differ in areas of primary neuropathology and clinical characteristics. Conventional CT scan interpretation, visual inspection of pictures, has not been useful in studying dementia. Recent studies of the digitally stored CT attenuation values have found systematic variations with normal aging and aphasia subtypes. In this study of numerical CT scan information in four Alzheimer's Disease and two Huntington's Disease patients, a double dissociation of frontal and temporal lobe density values was found, and a significant correlation was found between left temporal lobe density and verbal ability measures in the Alzheimer's Disease patients.     

Olfactory dysfunction in man: anatomical and behavioral aspects

We reviewed studies examining the olfaction of patients with brain damage for the purpose of discerning correlations between disordered structure and function. Patient samples included those with neurological disorders and neurosurgical interventions and recording of spontaneous or elicited neuronal activity. Brain areas involved in olfaction include the olfactory bulbs, the orbitofrontal and medial temporal cortices, the thalamus, and the amygdala. Despite recent advances in olfactory anatomy, understanding of how these structures are related to olfactory detection, discrimination, and recognition continues to be limited. Inadequate localization of brain lesions and lack of comprehensive behavioral assessment have thus far prevented a detailed account of the organization of olfaction in the human brain.     

Sex differences in behavioral and cognitive aspects of decision control

Sex differences in three components of decision control were examined in a series of studies utilizing 4-, 9-, and 14-year-old subjects. These components were actual decision control behavior, the cognitive understanding of the masculine or feminine nature of decision control, and the self-perception of decision control skills. At the behavioral level, boys controlled more decision outcomes than girls, especially at the oldest age grouping. In the area of self-perception, girls were less likely to perceive themselves as decision controllers compared to their male counterparts in the oldest age grouping. As far as general attitudes were concerned, neither boys nor girls equated decision control with masculinity. Results are discussed in terms of the socialization of powerlessness in women.     

Pictorial priming and cued recall in Alzheimer's and Huntington's disease

A picture fragment test was used to compare the priming and cued recall performances of patients with Huntington's disease (HD), patients with dementia of the Alzheimer type (DAT), and neurologically intact normal control (NC) subjects. On the pictorial priming test, subjects were asked to say "the first thing you think of" when shown incompletely drawn pictures, half of which were previously exposed to the subject during an unrelated naming task. Normal controls and HD patients, but not DAT patients, demonstrated similar increases in their ability to identify fragmented versions of previously seen pictures relative to novel pictures. These results are consistent with the previously observed pattern of preserved and impaired verbal priming ability in HD and DAT patients, respectively. The NC subjects, as expected, also demonstrated better performance on the cued recall than on the priming version of the picture fragment test, whereas the HD patients evidenced the opposite relationship on these two tasks and DAT patients were found to be equally impaired on both tests. This finding provides further support for the notion that HD patients' memory impairment is characterized primarily by an inability to initiate systematic retrieval strategies.