Biomedical subjects

Barbara J Knowlton

Publications and source records attributed to Barbara J Knowlton.

26 records · Page 2Linked to original sources

PubMed2004

A neurocomputational model of analogical reasoning and its breakdown in frontotemporal lobar degeneration.

Analogy is important for learning and discovery and is considered a core component of intelligence. We present a computational account of analogical reasoning that is compatible with data we have collected from patients with cortical degeneration of either their frontal or anterior temporal cortices due to frontotemporal lobar degeneration (FTLD). These two patient groups showed different deficits in picture and verbal analogies: frontal lobe FTLD patients tended to make errors due to impairments in working memory and inhibitory abilities, whereas temporal lobe FTLD patients tended to make errors due to semantic memory loss. Using the "Learning and Inference with Schemas and Analogies" model, we provide a specific account of how such deficits may arise within neural networks supporting analogical problem solving.

Aged↗

PubMed2003

Working memory and relational reasoning in Klinefelter syndrome.

Klinefelter syndrome (KS) is a sex chromosome abnormality associated with male infertility and mild cognitive deficits. Individuals with KS have been reported to have impaired verbal ability, as well as deficits in executive function. To further understand the nature of their deficits, we assessed specific elements of frontal lobe function such as working memory and relational reasoning. Men with KS exhibited a deficit in a transitive inference task in which participants ordered a set of names based on a list of propositions about the relative heights of the people named. This deficit was present even for items in which the propositions were given in order, so a chaining strategy could be used. Men with KS are also impaired on the n-back task, which uses letters as stimuli. In contrast, these men performed as well as controls in nonverbal reasoning (Raven's Progressive Matrices). These results suggest that men with KS have intact nonverbal reasoning abilities, but that a difficulty in encoding verbal information into working memory may underlie their executive and linguistic impairments.

Adult↗

PubMed2002

Learning and memory functions of the Basal Ganglia.

Although the mammalian basal ganglia have long been implicated in motor behavior, it is generally recognized that the behavioral functions of this subcortical group of structures are not exclusively motoric in nature. Extensive evidence now indicates a role for the basal ganglia, in particular the dorsal striatum, in learning and memory. One prominent hypothesis is that this brain region mediates a form of learning in which stimulus-response (S-R) associations or habits are incrementally acquired. Support for this hypothesis is provided by numerous neurobehavioral studies in different mammalian species, including rats, monkeys, and humans. In rats and monkeys, localized brain lesion and pharmacological approaches have been used to examine the role of the basal ganglia in S-R learning. In humans, study of patients with neurodegenerative diseases that compromise the basal ganglia, as well as research using brain neuroimaging techniques, also provide evidence of a role for the basal ganglia in habit learning. Several of these studies have dissociated the role of the basal ganglia in S-R learning from those of a cognitive or declarative medial temporal lobe memory system that includes the hippocampus as a primary component. Evidence suggests that during learning, basal ganglia and medial temporal lobe memory systems are activated simultaneously and that in some learning situations competitive interference exists between these two systems.

Animals↗

PubMed2002

Step training with body weight support: effect of treadmill speed and practice paradigms on poststroke locomotor recovery.

OBJECTIVE: To investigate the effect of practice paradigms that varied treadmill speed during step training with body weight support in subjects with chronic hemiparesis after stroke. DESIGN: Randomized, repeated-measures pilot study with 1- and 3-month follow-ups. SETTING: Outpatient locomotor laboratory. PARTICIPANTS: Twenty-four individuals with hemiparetic gait deficits whose walking speeds were at least 50% below normal. INTERVENTION: Participants were stratified by locomotor severity based on initial walking velocity and randomly assigned to treadmill training at slow (0.5mph), fast (2.0mph), or variable (0.5, 1.0, 1.5, 2.0mph) speeds. Participants received 20 minutes of training per session for 12 sessions over 4 weeks. MAIN OUTCOME MEASURE: Self-selected overground walking velocity (SSV) was assessed at the onset, middle, and end of training, and 1 and 3 months later. RESULTS: SSV improved in all groups compared with baseline (P<.001). All groups increased SSV in the 1-month follow-up (P<.01) and maintained these gains at the 3-month follow-up (P=.77). The greatest improvement in SSV across training occurred with fast training speeds compared with the slow and variable groups combined (P=.04). Effect size (ES) was large between fast compared with slow (ES=.75) and variable groups (ES=.73). CONCLUSIONS: Training at speeds comparable with normal walking velocity was more effective in improving SSV than training at speeds at or below the patient's typical overground walking velocity.

Adult↗

PubMed2002

The effect of testing procedure on remember-know judgments.

Remember-know (R-K) judgments are commonly used to assess conscious recollection of the study episode during recognition. We varied whether participants judged items as R, K, or new (one-step) or first made an old-new judgment and then made the R-K judgment (two-step). The one-step group had a higher R hit rate and K false alarm rate than did the two-step group. In addition, the K responses of the one-step group did not reliably discriminate between old and new items. When a "guess" response category was available, both groups were able to discriminate old and new items using the K response; however, K responses remained more accurate in the two-step condition. R responses appeared to be relatively immune to the effects of testing procedure when the guess category was provided. This suggests that, under some conditions, the R label can reliably indicate a distinct form of recognition memory, suggesting that allowing participants to use a guess response may help them to confine their R-Kjudgments to confidently recognized items. When participants are not given the option of making a guess response, they may use the R-K distinction to indicate the trace strength of the memory.

Cognition↗

PubMed2002

Intact implicit habit learning in Alzheimer's disease.

Habit learning refers to the incremental implicit learning of associations. Patients with Alzheimer's disease (AD) exhibit deficits in explicit memory and in conceptual implicit memory tasks that rely on the cortical areas damaged in AD. The authors tested patients with AD and controls on a probabilistic classification task in which participants implicitly acquire cue-outcome associations. Both groups showed evidence of learning across 50 trials, and performance did not differ significantly between the groups. In contrast, patients with AD exhibited a profound impairment in explicit memory for the testing episode. These results are consistent with the idea that habit learning relies on subcortical structures, including the basal ganglia, and is independent of the medial temporal and cortical areas damaged in AD.

Aged↗

PubMedDate not supplied

Analysis of probabilistic classification learning in patients with Parkinson's disease before and after pallidotomy surgery.

This study examined the characteristics of probabilistic classification learning, a form of implicit learning previously shown to be impaired in patients with basal ganglia dysfunction (e.g., Parkinson's disease). In this task, subjects learn to predict the weather using associations that are formed gradually across many trials, because of the probabilistic nature of the cue-outcome relationships. Patients with Parkinson's disease, both before and after pallidotomy, and age-matched control subjects, exhibited evidence of probabilistic classification learning across 100 training trials. However, pallidotomy appears to hinder the learning of associations most implicit in nature (i.e., weakly associated cues). Although subjects were most sensitive to single-cue associations when learning the task, there is evidence that cue combinations contribute significantly to probability learning. The utility of multiple dependent measures is discussed.

Aged↗

PubMedDate not supplied

Contributions of striatal subregions to place and response learning.

The involvement of different subregions of the striatum in place and response learning was examined using a T-maze. Rats were given NMDA lesions of the dorsolateral striatum (DLS), anterior dorsomedial striatum (ADMS), posterior dorsomedial striatum (PDMS), or sham surgery. They were then trained to retrieve food from the west arm of the maze, starting from the south arm, by turning left at the choice point. After 7 d of training, with four trials a day, a probe test was given in which the starting arm is inserted as the north arm, at the opposite side of the maze. A left turn would indicate a "response" strategy; a right turn, a "place" strategy. The rats were then trained for 7 more days, followed by a second probe test. Unlike rats in the other groups, most of the rats in the PDMS group turned left, using the response strategy on both probe tests. These results suggest that the PDMS plays a role in spatially guided behavior.

Animals↗