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The biological basis of incremental learning

Reward-related processing in Parkinson's Disease

Intervention strategies that enhance learning

The functional neuroanatomy of articulatory rehearsal

Articulatory and phonological processes in working memory: effects of brain damage

The neural basis of lexical processing

Interactive processes in language: sentence processing

The goal of this project is to understand the roles of both cortical and subcortical brain regions in incremental learning, which is the acquisition of perceptual discriminations, stimulus associations, and motor skills through repetitive experience, as demonstrated in the behavior of both humans and animals. In these studies, normal adults perform cognitive operations with visual and auditory stimuli while maintaining central eye fixation. We examine how different stimulus and task conditions produce different patterns of behavioral performance (e.g., increases in errors) and functional brain activation.

The specific objectives of the proposed work are:

1) to develop human analogues of tasks used to explore reward-based incremental learning in rats and monkeys, in order to facilitate inter-species comparisons.

2) to identify brain regions which show reward-related activity, and to explore the temporal characteristics of this activity across a single trial.

3) to determine whether the temporal characteristics of reward-related activity change as the reward becomes associated with a particular stimulus.

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Neurophysiological and lesion studies in animals have implicated the striatum as a major component in motivational behavior and reward-related processing. Converging lesion data indicates that lesions to either the dorsal or the ventral striatum affect motivated behavior. We hypothesize that reward-related responses that we have observed in the striatum reflect modulatory input from dopamine neurons in the brainstem. One way to test this hypothesis with imaging is to determine whether the observed reward-related responses are affected by changes in tonic stimulation of the dopamine system, and by changes in the capacity of the system to mount a phasic response. We propose that Parkinson's Disease presents a system in which both of these factors can be independently modulated.

Our goals in this research are:

1) to determine if manipulations that affect the firing rate of dopaminergic brainstem neurons affect functional activity in the striatum.

2) to determine whether manipulations which affect the release and/or binding of dopamine alter activation in the striatum.

3) to demonstrate that dynamic changes in the firing of brainstem dopamine neurons underlie dynamic modulation of striatal activity.

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An important prerequisite for language comprehension and the acquisition of reading is adequate speech discrimination ability. Recent research suggests that perceptual mechanisms for speech discrimination may be more adaptable than previously thought, and that both for children and adults intervention strategies may be effective at remediating deficiencies in the discrimination and representation of speech sounds (Tallal et al., 1996). We test principles of perceptual learning through studies which attempt to induce plasticity in the speech discrimination abilities of adult Japanese subjects. Specifically, these include the principles that plasticity is best induced by procedures that maintain high levels of accurate task performance, that learning should progress incrementally beginning with stimuli that are initially easy and on the extreme of the perceptual continuum towards stimuli that are more difficult contrasts, that feedback is important for learning to occur, and that cues from other modalities may enhance the learning rate.

This line of research attempts:

1) To investigate the effectiveness of different behavioral intervention strategies designed to improve speech discrimination; specifically, we will teach adult speakers of Japanese to discriminate between the sound of /r/ and the sound of /l/.

2) To investigate the neural basis for effective and ineffective training regimes, by using functional brain imaging to identify regions whose activity is modified as a result of training.

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The research program involves a sequence of experiments utilizing behavioral and topographic fMRI methods to localize brain regions involved in articulatory rehearsal and other types of articulatory and phonological processing. The investigations of stimulus effect (such as the word length effect) as well as other task manipulations (such as concurrently articulating the word "the") provide the potential to fractionate the different components of the articulatory rehearsal system using both behavioral and neuroimaging techniques. This research program will enhance our understanding of those brain regions which support verbal working memory, a critical ability which has been tied to skilled reading and comprehension. Such knowledge may ultimately aid in the development of enhanced instructional methods and improved remediation of subjects with brain damage.

1) The replication of previous fMRI and positron emission tomography (PET) studies involving verbal working memory tasks.

2) The extension of previous fMRI results through the use of different stimulus conditions in a verbal working memory task, which involves articulatory rehearsal.

3) More accurate identification, localization, and characterization of the brain regions which support articulatory rehearsal, such as the left frontal cortex and the cerebellum.

4) The use of behavioral testing to further explore the implications of the neuroimaging results and to refine cognitive psychological models of the articulatory rehearsal system.

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We hypothesize that damage to brain regions involved in verbal rehearsal will result in an impaired ability to perform verbal working memory tasks, and some speech production and phonological analysis tasks. This behavioral and functional imaging work is closely tied to neuroimaging and behavioral data collected in young normal subjects, and will thus be instrumental in enhancing our understanding of brain regions that support normal working memory function. Results from this research program may eventually advance our understanding and treatment of working memory and language impairments in children and adults with acquired brain damage.

Specifically, our aims are:

1) to determine whether damage to the temporo-parietal cortex, the left inferior frontal gyrus (Broca's area) and the cerebellum produces impairments on tests of verbal working memory .

2) to determine whether deficits in verbal working memory co-occur with deficits in speech production, reading, and/or phonological analysis.

3) to determine whether there are differences in the patterns of impaired and preserved performance following left frontal versus cerebellar damage.

4) to identify brain regions involved in the verbal working memory rehearsal system and to see if previously identified areas are active in these tasks.

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The objective of this research program is to understand the neural basis of single word processing, which involves understanding the phonological (word sound), orthographic (word form), semantic (word meaning), and morphological (word grammar) components of perceiving, comprehending, and producing words). This combination of behavioral and neuroimaging work is closely tied to previously collected neuroimaging and behavioral data and to future studies of both kinds. Normal adults perform cognitive operations with visual and auditory stimuli while maintaining central eye fixation. We examine how different stimulus and task conditions produce different patterns of behavioral performance.

This study aims:

1) To explore subjects' ability to process phonological, orthographic, semantic, and morphological features of visually and auditorily presented words, by evaluating different task conditions and the effects of different stimulus manipulations.

2) To extend previous neuroimaging and behavioral results by having subjects perform related tasks designed to further investigate cognitive explanations for specific regions of brain activation.

3) To investigate the role of specific brain regions in acquiring and reading a second language and to use this information to better understand general language processing

Our current research involves a neuroimaging investigation of the visual word form area. The recruitment of both Chinese participants and native English speakers will allow us to probe for differences in processing of linguistic stimuli across languages. Several concomitant behavioral studies are also being conducted to validate the result of findings in neuroimaging.

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Given recent views of sentence processing and working memory, we can reconsider the role of phonological representations in sentence-level language comprehension. New perspectives suggest that the question of whether or not working memory is "used" in sentence processing is misplaced: rather, language comprehension and production involve the mapping between phonological and semantic representations, and this mapping can also be extended to assessments of memory in the laboratory.

Our objectives include:

1) to explore the extent to which phonological activation contributes to sentence processing.

2) to determine whether a subset of the brain regions that are active during sentence processing will show increased activity under conditions of phonological overlap.

3) to investigate whether the regions most affected by phonological similarity will be regions that are active during phonological working memory tasks in normal subjects.

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