Dementia rating scale performance: a comparison of vascular and Alzheimer's dementia.

Differences in the pattern of neuropsychological dysfunction associated with Alzheimer's disease (AD) and vascular dementia (VaD) were examined using the Dementia Rating Scale (DRS). We examined three groups of patients: (1) Patients with AD; (2) patients with single stroke (CVA); and (3) patients with multiple cerebral infarctions (MI). Comparisons of cognitive dysfunction were conducted on patients that met the DRS criteria for dementia. Dementia groups were similar in age, education, and severity of dementia. Comparisons of the AD and two VaD groups across the specific DRS-scales (Attention, Conceptualization, Construction, Initiation/Perseveration, and Memory) indicated that patients with AD were more impaired on the DRS-Memory while the patients with VaD were more impaired on the DRS-Construction. Additionally, patients with VaD related to MI scored lower on the DRS-Initiation/Perseveration as compared to patients with AD, and patients with AD scored lower on the DRS-Conceptualization as compared to patients with VaD related to CVA. These results are indicative of qualitative differences in the pattern of cognitive deficits associated with the two types of dementia.

The naming deficit in early Alzheimer's and vascular dementia.

Patients with early Alzheimer's disease (AD) were compared to normal controls and patients with early vascular dementia (VaD) on their naming errors using the Boston Naming Test (H. Goodglass & E. Kaplan, 1983). All naming errors were classified into three general error categories: visuoperceptual, semantic, and phonemic. Semantic errors were further classified into coordinate errors (responses that belong to the same semantic category as the target words), superordinate errors (responses that belong to a broader semantic category than the target word), and functional-circumlocutory errors (circumlocutions and responses that functionally describe the target word). The findings indicated that AD participants display more overall naming errors than VaD participants, although the pattern of general errors was similar between the patient groups. However, the qualitative difference between the patient groups was observed within the semantic errors because the AD group made more superordinate errors.

Cross-correlation and microstimulation: complementary tools in the extracellular analysis of synaptic interactions.

The utility of extracellular microstimulation as an ancillary tool to compliment cross-correlation analyses is explored. This technique aims at demonstrating the "sufficiency' of the spike train generated by the "reference' neuron in eliciting spikes in the "target' neuron. It involves activating the reference neuron with very low-intensity current pulses (1-10 microA) delivered through the recording microelectrode. Microstimulation can provide independent evidence that can either support or refute notions of synaptic connectivity generated by correlation analyses. Data are presented from antidromically identified descending corticofugal neurons and putative inhibitory interneurons of S1 "barrel' cortex of the rabbit and from simultaneously recorded neurons in the topographically aligned "barreloid' of ventroposterior medial thalamus (VPM). A very strong relationship was seen between brief, statistically significant peaks in the cross-correlograms (CCGs) suggestive of monosynaptic excitatory input and the responses of cortical neurons to VPM microstimulation. Thus, 18/19 cortical neurons that responded to microstimulation pulses of < 6 microA showed a significant CCG with the VPM neuron. Conversely, each of 16 cortical neurons that failed to respond at 10 microA also failed to show a significant CCG. CCGs compiled from independent data sets collected before and after hundreds of microstimulation pulses were very similar, showing that such stimulation can be relatively benign. The method has many limitations, which are discussed. The most serious problem is that the effects of extracellular current pulses cannot be limited to the reference neuron. Nevertheless, microstimulation can provide independent experimental support or refutation of hypotheses of synaptic connectivity that are generated by cross-correlation analyses. In addition, since the technique is rapidly implemented and has considerable power to predict significant cross-correlations, it can be useful in deciding which neuron pairs to study when limited time is available for data collection.

Syntactic processing in agrammatic aphasia by speakers of a Slavic language.

It is widely believed that agrammatic aphasics have lost the ability to assign complete syntactic representations. This view stems from indications that agrammatics often fail to comprehend complex syntactic structures, as for example, some types of relative clauses. The present study presents an alternative account. Comprehension by Serbo-Croatian-speaking agrammatic aphasics was tested on four types of relative clause structures and on conjoined clauses. The relative clauses varied in type of embedding (embedded vs. nonembedded) and in the location of the gap (subject position vs. object position). There were two control groups: Wernicke-type aphasics and normal subjects. The findings from a sentence-picture matching task indicated that agrammatic aphasics were able to process complex syntactic structures, as evidenced by their well-above chance performances. The success rate varied across different types of relative clauses, with object-gap relatives yielding more errors than subject-gap relatives in all groups. Each group showed the same pattern of errors: agrammatic subjects were distinguished from Wernicke subjects and normal subjects only in quantity of errors. These findings are incompatible with the view that the agrammatics are missing portions of the syntax. Instead, their comprehension deficits reflect varying degrees of processing impairment in the context of spared syntactic knowledge.

Reduction in alphabet priming with delay and degradation.

Phonologically ambiguous Serbo-Croatian words are named more slowly than their phonologically unique partners. This difference is reduced by nonword primes containing consonants unique to one or the other alphabet. In 2 experiments we investigated the hypothesis that alphabet priming is the inhibition of unique and ambiguous letter units of one alphabet by the unique letter units of the other alphabet. In Experiment 1, ambiguous and unique words followed alphabet-specific nonwords at lags between 100 ms and 1,550 ms. The ambiguous-unique difference increased from 1 ms to 45 ms, consistent with a relaxing inhibitory process. In Experiment 2 we compared priming of ambiguous words with and without visual noise. Priming was less for noisy than for intact stimuli, as would be expected if noise slows processing and if the inhibition responsible for priming weakens further during the additional processing time.

Further evidence for phonological constraints on visual lexical access: TOWED primes FROG.

If the phonological codes of visually presented words are assembled rapidly and automatically for use in lexical access, then words that sound alike should induce similar activity within the internal lexicon. TOWED is homophonous with TOAD, which is semantically related to FROG, and BEACH is homophonous with BEECH, which is semantically related to TREE. Stimuli such as these were used in priming-of-naming task, in which words homophonous with associates of the target words preceded the targets at an onset asynchrony of 100 msec. Relative to spelling controls (TROD, BENCH), the low-frequency TOWED and the high-frequency BEACH speeded up the naming of FROG and TREE, respectively, to the same degree. This result was discussed in relation to the accumulating evidence for the primacy of phonological constraints in visual lexical access.

Sensitivity to inflectional morphology in agrammatism: investigation of a highly inflected language.

We present the results of a study with six Serbo-Croatian-speaking agrammatic patients on a test of inflectional morphology in which subjects judged whether spoken sentences were grammatical or ungrammatical. Sensitivity to two kinds of syntactic features was investigated in these aphasic patients: (1) subcategorization rules for transitive verbs (which must be followed by a noun in the accusative case; intransitive verbs can be followed by nouns in other noun cases); (2) sensitivity to the inflectional morphology marking noun case. The test items consisted of three-word sentences (noun-verb-noun) in which verb transitivity and appropriateness of the case inflection of the following noun were manipulated. Results of the grammaticality judgment task show that both syntactic properties are preserved in these patients.

Grammatical priming of inflected nouns by the gender of possessive adjectives.

Two experiments examined the effect on lexical decision times for inflected Serbo-Croatian nouns when the nouns were preceded by possessive adjectives (my, your, our). For any given pairing the possessive adjective and the noun agreed always in number (singular) and case (nominative) but only agreed half of the time in gender (masculine or feminine). Lexical decisions were faster when the noun targets were of the same gender as their primes. This gender congruency/incongruency effect was shown to hold whether the inflections of the adjective and noun were the same (as is the case for typical Serbo-Croatian nouns) or different (as is the case for atypical Serbo-Croatian nouns). The results are discussed in terms of a postlexical influence of grammatical processing on the recognition of individual words.