Biomedical subjects

N Stolar

Publications and source records attributed to N Stolar.

6 recordsLinked to original sources

PubMed1999

Word production in schizophrenia and its relationship to positive symptoms.

We explored relationships between positive symptoms of schizophrenia and neurocognitive functions (language and memory). The semantic and phonemic associations among words produced in a verbal fluency task by 26 participants diagnosed with DSM-III-R schizophrenia were examined. Formal thought disorder was associated with producing fewer contextually related words and with producing more unrelated words. In contrast, hallucinations were associated with producing more related words. Our results suggest associations between formal thought disorder and impaired memory, and between hallucinations and increased lexical activation/excessive synaptic pruning.

Adult↗

PubMed1994

Neuropsychological correlates of alogia and affective flattening in schizophrenia.

We examined whether two negative symptoms, alogia and affective flattening, were more strongly associated with dysfunction of certain brain regions than with others in a sample of 27 schizophrenic subjects. Neuropsychological tests were used to measure the integrity of functioning of different brain regions. Functioning of left and right frontal regions was assessed by word fluency and design fluency, respectively, and functioning of the left temporo-hippocampal region was assessed by Hebb's digit-sequences recall test. Measures of alogia and affective flattening were obtained using the Scale for the Assessment of Negative Symptoms. The results indicated that more severe levels of these negative symptoms were associated with poorer performance on the fluency tests. These relationships were fairly specific as indicated in two ways: (1) only certain neuropsychological measures were associated with negative symptoms; and (2) poor performance on fluency tests was not associated with all psychiatric symptoms. In addition, affective flattening, but not alogia, appeared to be associated with lateralized dysfunction.

Adult↗

PubMed1992

Variations in lateralized processing among right-handers: effects on patterns of cognitive performance.

Two experiments investigated whether individual differences among right-handers in patterns of lateralized processing were related to level of performance on a variety of cognitive tasks presented under non-tachistoscopic conditions. Subjects were divided into two groups of individuals, those who characteristically have greater than average right-hemisphere involvement in functioning and those who characteristically have greater than average left-hemisphere involvement. In the first experiment we examined whether characteristic individual differences in hemispheric involvement could predict performance on a facial memory task. The group with relatively greater right-hemisphere involvement had better recognition memory than the group with relatively greater left-hemisphere involvement. In the second experiment, we examined whether individual differences in hemispheric involvement could predict performance on a larger set of cognitive tasks. The groups were administered two tasks selected to evaluate left-hemisphere function and two selected to evaluate right-hemisphere function. The results indicated that the groups differed in their profile of cognitive performance. Individuals with greater than average right-hemisphere involvement in processing tended to perform better on tasks indexing right-hemisphere function than on tasks indexing left-hemisphere function, whereas the opposite was true of individuals with greater than average left-hemisphere involvement. Collectively, the results of these two experiments indicate that individual differences in lateralized performance have important implications for individual differences in patterns of cognitive ability.

Adult↗

PubMed1990

Interhemispheric processing in left- and right-handers.

Inter- and intrahemispheric processing for left- and right-handers were compared in two experiments. In one, subjects performed a digit-matching task and in the other they decided if two letters were part of a previously presented word. On some trials the matching items were presented initially only to one hemisphere (within-hemisphere trials), and hence the match decision could be reached by a hemisphere in isolation. On other trials, one item of the match pair was presented to each hemisphere (across-hemisphere trials), requiring interhemispheric interaction for the match decision. Patterns of performance on within-as compared to across-hemisphere trials were identical for the two handedness groups in both experiments. Furthermore, individual characteristics of subjects such as their hand posture, sex and family history of left-handedness did not affect the pattern of performance. These results suggest that interhemispheric processing may not differ between right- and left-handers.

Brain↗

PubMed1989

Conditional stimulus probability and activity of hippocampal, cingulate cortical, and limbic thalamic neurons during avoidance conditioning in rabbits.

Past studies of the neuronal correlates of avoidance conditioning in rabbits have led to a model of information flow among structures of the limbic system. A hypothesis of the model is that unexpected stimuli activate certain hippocampal and cingulate cortical neurons. This activity in turn suppresses or "limits" the firing of limbic thalamic neurons. This hypothesis is tested in relation to stimuli classified as unexpected or expected on the basis of their incidence or "probability." Multi-unit and field potential responses in the anterior and posterior cingulate cortices (AC and PC), the dentate gyrus (DG), and the anterior ventral (AV) and medial dorsal (MD) thalamic nuclei were recorded during the acquisition and performance of a locomotor conditioned response (CR). The CR, stepping in an activity wheel in response to a 0.5-s tone (CS+), prevented the occurrence of a shock US scheduled 5 s after CS+ onset. The rabbits also learned to ignore a different tone (CS-), not predictive of the US. Training was given daily (120 trials, 60 with each CS in an irregular sequence) until behavioral discrimination reached criterion. After criterion, asymmetric probability (AP) sessions were given, in which the CS+/CS- proportions were .2/.8 or .8/.2. The AP sessions were the same as conditioning sessions except for the probability manipulation. A significant discriminative response, i.e., a greater neuronal discharge to the CS+ than to the CS-, developed in all regions during behavioral acquisition. The unit response in the AP sessions was enhanced in all areas by rare presentation of the CS-, compared with the equal and frequent CS- conditions. Rare presentation of the CS+ enhanced the unit response in the cortical areas (AC, PC, and DG), but it suppressed the firing of limbic thalamic (AV and MD) neurons. These results were supportive of the model. Rare CS+ presentations did not alter AV and PC neuronal activity in rabbits with subicular lesions, a result suggesting that an intact hippocampus is essential for normal neuronal responses to stimulus probability in the cingulate cortex and limbic thalamus.

Animals↗

PubMed1987

Hippocampal control of cingulate cortical and anterior thalamic information processing during learning in rabbits.

Past studies of the neural determinants of discriminative avoidance conditioning in rabbits have fostered a theoretical model that describes the interactive functioning of the cingulate cortex (Brodmann's Areas 24 and 29), the anterior ventral and medial dorsal thalamic nuclei (AVN and MDN) and the hippocampus. Here we test hypotheses of the model concerning the influence of the hippocampus on cortical and thalamic information processing. The rabbits learned to perform locomotory conditioned responses (CRs) in an activity wheel in response to an acoustic (pure tone) positive conditional stimulus (CS+). A shock unconditional stimulus (US) was given 5 s after CS+ onset, but locomotion during the CS+ - US interval prevented the US. The rabbits also learned to ignore a second tone (a negative conditional stimulus, CS-) of different auditory frequency than the CS+, that did not predict the US. Multi-unit activity and intracranial macropotentials were recorded in the cingulate cortex and the AVN during acquisition, overtraining, extinction, reacquisition and reversal training. Data were obtained in intact rabbits and in rabbits with bilateral lesions of the subicular complex, the origin of projections of the hippocampal formation to the cingulate cortex and AVN. In addition, the activity in the AVN was recorded in a separate group of rabbits with posterior cingulate cortical (Area 29) lesions. Subicular and Area 29 lesions were associated with an enhancement of the training-induced CS+ elicited neuronal response in the AVN. The frequency of CRs was enhanced in animals with subicular lesions. CS elicited unit responses in the cingulate cortices were attenuated in rabbits with subicular lesions. Both of the lesions were associated with significantly increased amplitudes of the CS elicited average cortical and thalamic macropotentials. These results suggested the following conclusions: subiculocortical afferents provide an enabling influence that is essential for CS elicited excitation in the cingulate cortex; the cingulate cortical excitatory response in intact animals exerts a limiting influence on the activity in the AVN; the enhanced AVN neuronal response in rabbits with lesions is due to the absence of the limiting influence and it contributes to the increased CR frequency in those animals. It is hypothesized that the hippocampus via subiculocortical projections, governs the flow of CR-inducing thalamocortical excitatory volleys. This governance determines the timing of CR output. The results of hippocampal processing of contextual information acting through the subiculocortical projection determines the moment most appropriate for the CR.

Acoustic Stimulation↗