Dynamic-intentional thalamic aphasia: a failure of lexical-semantic self-activation.

BACKGROUND: Previous research has described patients with aphasia from thalamic lesions, some of whom were non-fluent with intact comprehension, others who were fluent with impaired comprehension, and some of whom are non-fluent with impaired comprehension. Whereas these three subtypes usually have normal repetition, they had impaired naming, suggesting a deficit in lexical (phonological word forms)-semantic processing. We report a patient with a left thalamic hemorrhage in which lexical-semantic representations appear to be intact but the patient demonstrates an inability to spontaneously activate his lexical-semantic system. METHODS: A 82-year-old, right-handed man presented with decreased verbal fluency and memory loss following a thalamic hemorrhage. Neuropsychological assessment revealed significant decrements in verbal fluency with intact naming, comprehension, repetition and vocabulary. CONCLUSIONS: To the best of our knowledge this pattern of language disturbance, which mirrors dynamic aphasia induced by frontal lesions, has not previously been described with thalamic injury. The thalamus has strong connections with the frontal lobe and rather than degradation of lexical-semantic representations, this patient's thalamic lesion probably induced frontal lobe dysfunction with a failure to spontaneously active lexical semantic representations.

Sensory-spatial transformations in the left posterior parietal cortex may contribute to reach timing.

The posterior parietal cortex (PPC) contains viewer-centered spatial maps important for reaching movements. It is known that spatial reaching deficits emerge when this region is damaged, yet less is known about temporal deficits that may also emerge because of a failure in sensory-spatial transformations. This work introduces a new geometric measure to quantify multimodal sensory transformation and integration deficits affecting the tempo of reaching trajectories that are induced by injury to the left PPC. Erratic rates of positional change involving faulty maps from rotational angular displacements to translational linear displacements contributed to temporal abnormalities in the reach. Such disruptions were quantified with a time-invariant geometric measure. This measure, paired with an experimental paradigm that manipulated the source of visual guidance for reaches, was used to compare the performance of normal controls to those from a patient (T.R.) who had a lesion in his left-PPC. For controls, the source of visual guidance significantly scaled the tempo of target-directed reaches but did not change the geometric measure. This was not the case in patient T.R., who altered this measure. With continuous, extrapersonal visual feedback of the target, however, these abnormalities improved. Vision of the target rather than vision of his moving hand also improved his arm-joint rotations for posture control. These results show that the left PPC is critically important for visuo-motor transformations that specifically rely on extrapersonal cues to align rotational-arm and linear-hand displacements and to continuously integrate their rates of change. The intactness of this system contributes to the fluidity of the reach's tempo.

Progressive asymmetric apraxic agraphia.

BACKGROUND/OBJECTIVES: Patients with apraxic agraphia cannot correctly form the letters needed to write words but can correctly spell words orally. Apraxic agraphia (AA) is often associated with ideomotor apraxia and most commonly induced by stroke, but can be associated with degenerative diseases. In degenerative diseases, asymmetrical apraxic agraphia (AAA) has rarely been reported as one of the presenting features. The purpose of this report is to describe a case series of 3 patients who presented with an AAA, and also to elucidate some of the cognitive mechanisms of this disorder. METHODS/RESULTS: These patients, who were not aphasic or alexic, developed agraphia as one of their earliest reported symptoms. They also demonstrated an asymmetrical ideomotor apraxia. Their agraphia was characterized by the inability to form letters, with the preserved ability to orally spell. To learn if this disorder was being caused by a loss of spatial-movement representations versus an impairment of implementation, one patient was asked to determine if gestures made by the examiner were correct or incorrect, and also to image the structure of letters. He performed poorly on both these tests and he also demonstrated an asymmetrical agraphesthesia. CONCLUSIONS: These patients' AAA might be the beginning of the corticobasal degeneration syndrome, but future studies will have to examine the brain pathology associated with AAA. Our patient's poor performance on pantomime recognition and imagery suggests that his apraxia is related to a deterioration of his graphemic and transitive spatial movement representations. The recognition of numbers written on the hand with eyes closed might also depend on having intact movement representations and his asymmetrical agraphesthesia might also be related to his AAA.

Defective comprehension of emotional faces and prosody as a result of right hemisphere stroke: modality versus emotion-type specificity.

Studies of patients with brain damage, as well as studies with normal subjects have revealed that the right hemisphere is important for recognizing emotions expressed by faces and prosody. It is unclear, however, if the knowledge needed to perform recognition of emotional stimuli is organized by modality or by the type of emotion. Thus, the purpose of this study is to assess these alternative a priori hypotheses. The participants of this study were 30 stroke patients with right hemisphere damage (RHD) and 31 normal controls (NC). Subjects were assessed with the Polish adaptation of the Right Hemisphere Language Battery of Bryan and the Facial Affect Recognition Test based on work of Ekman and Friesen. RHD participants were significantly impaired on both emotional tasks. Whereas on the visual-faces task the RHD subjects recognized happiness better than anger or sadness, the reverse dissociation was found in the auditory-prosody test. These results confirm prior studies demonstrating the role of the right hemisphere in understanding facial and prosodic emotional expressions. These results also suggest that the representations needed to recognize these emotional stimuli are organized by modality (prosodic-echoic and facial-eidetic) and that some modality specific features are more impaired than others.

The influence of vagus nerve stimulation on memory.

BACKGROUND: Vagus nerve stimulation (VNS) has been shown to improve memory. OBJECTIVE: The purpose of this study was to learn at which stage of memory formation this influence occurs. METHODS: Ten subjects who had been implanted with vagus nerve stimulators for the treatment of intractable seizures performed tasks that assessed learning and retention (Hopkins Verbal Learning Test) during actual and sham VNS. RESULTS: We found that VNS had no effect on learning but enhanced consolidation, which led to improved retention. CONCLUSIONS: The means by which VNS improves retention is probably related to the increased activity in the nucleus of the tractus solitarius and the locus coeruleus-central adrenergic system that activates the amygdala and increases long-term potentiation in the hippocampus.

Effect of vagus nerve stimulation on creativity and cognitive flexibility.

OBJECTIVE: The purpose of this study was to determine whether vagus nerve stimulation influences cognitive flexibility and creativity. METHODS: Ten subjects, in whom vagus nerve stimulators had been implanted for the treatment of intractable seizures, performed tasks that assessed cognitive flexibility (solving anagrams), creativity (Torrance Test), and memory (Hopkins Verbal Learning Test) during actual and sham vagus nerve stimulation. RESULTS: Vagus nerve stimulation impaired cognitive flexibility and creativity, but these results could not be explained by the induction of a general encephalopathy because VNS did not impair learning and improved retention. CONCLUSIONS: The means by which vagus nerve stimulation impairs cognitive flexibility and creative thinking is probably related to increased activity of the locus coeruleus-central adrenergic system that increases the signal-to-noise ratio and improves the brain's ability to attend to sensory input, but decreases its ability to recruit large-scale networks.

Eye patching biases spatial attention after thalamic hemorrhage in a patient without spatial neglect: a case report.

Monocular patching has been advocated as a treatment for spatial neglect. Eye patching, however, is also reported to increase spatial bias. Thus, patching brain injury patients for ocular conditions may also impair their attention. To learn if an eye patch may induce asymmetric attention in a patient without spatial neglect, we tested a woman with diplopia after a left thalamic-intraventricular hemorrhage. She had no spatial neglect on bedside attention tasks. Using a laser pointer, she bisected a blank space at near (279 mm) and far (914 mm) distances under 3 conditions: unpatched and wearing a right or left eye patch. Unpatched, she showed no bias. She erred further leftward with right patching at both distances. Right eye patching appeared to induce neglect of right space when the patient performed this task. With left patching, leftward error tended to increase in near space only. Clinicians prescribing eye patches to patients with brain injury even for purely ocular indications, should evaluate them for spatial neglect once the patch is in place.

Treatment of pseudobulbar laughter after gamma knife thalamotomy.

We describe a case of pathological laughter after gamma knife thalamotomy which resolved after treatment with sertraline. It is important to identify this potentially treatable complication of surgical therapy.

Emotional experience and perception in the absence of facial feedback.

The facial feedback hypothesis suggests that facial expressions are either necessary or sufficient to produce emotional experience. Researchers have noted that the ideal test of the necessity aspect of this hypothesis would be an evaluation of emotional experience in a patient suffering from a bilateral facial paralysis; however, this condition is rare and no such report has been documented. We examined the role of facial expressions in the determination of emotion by studying a patient (F.P.) suffering from a bilateral facial paralysis. Despite her inability to convey emotions through facial expressions, F.P. reported normal emotional experience. When F.P. viewed emotionally evocative slides her reactions were not dampened relative to the normative sample. F.P. retained her ability to detect, discriminate, and image emotional expressions. These findings are not consistent with theories stating that feedback from an active face is necessary to experience emotion, or to process emotional facial expressions.