Reading with the right hemisphere: evidence from transcranial magnetic stimulation.

Although many patients with dominant hemisphere damage retain some reading ability, the anatomic substrate of the preserved reading remains controversial. We tested the hypothesis that the right hemisphere mediates the reading of some patients with acquired dyslexia by using Transcranial Magnetic Stimulation (TMS) to assess the effect of transient cortical stimulation on reading. A patient with (partially recovered) pure alexia was asked to read aloud briefly presented words, half of which were shown in association with TMS of the right or left hemisphere. Consistent with the right hemisphere reading hypothesis, stimulation of the right but not the left hemisphere disrupted oral reading.

Reading in pure alexia. The effect of strategy.

A number of investigators have demonstrated that patients with pure alexia comprehend briefly presented words which they are unable to explicitly identify. We suggested previously that these patients may read by means of two distinct procedures: a laborious letter-by-letter method and a 'whole-word' procedure which, at least initially, does not support explicit word identification. We report a test of this proposal in a patient with pure alexia. We reasoned that if the patient had access to two distinct and incompatible procedures, he might be induced to switch from one to the other by changing task demands. We found that when instructed to name words, the patient employed a letter-by-letter strategy; in contrast, when instructed to make lexical decision or semantic judgements about rapidly presented words, he appeared to use a 'whole-word' strategy. These data support the hypothesis that two distinct procedures are available to this patient. We argue, further, that is necessary to suppress use of the letter-by-letter strategy to demonstrate whole word reading capability in pure alexics, and that failure to do so may account for negative findings in other cases reported in the literature.

Frontal verbal amnesia. Phonological amnesia.

Although aphasic patients with frontal lobe damage may demonstrate impaired retention of verbal material, significant anterograde memory disturbances have not, to our knowledge, been reported with a minor Broca's aphasia. We describe a patient with minor Broca's aphasia who exhibited an unusual and profound anterograde memory disturbance, especially for phonologically specified stimuli. We suggest that this disturbance is attributable to an impairment in the volitional, controlled search of stored phonological information.

Simultanagnosia. To see but not two see.

Simultanagnosia is a disorder of visual perception characterized by the inability to interpret complex visual arrays despite preserved recognition of single objects. We report a series of investigations on a simultanagnosic patient which attempt to establish the nature of this visual processing disturbance. The patient performed normally on a feature detection task but was impaired on a test of attention-requiring visual search in which she was asked to distinguish between stimuli containing different numbers of targets. She was not impaired on a visual-spatial orienting task. She identified single briefly presented words and objects as rapidly and reliably as controls suggesting that access to stored structural descriptions was not impaired. With brief, simultaneous presentation of 2 words or drawings, she identified both stimuli significantly more frequently when the stimuli were semantically related than when they were unrelated. On the basis of these and other data, we suggest that the patient's simultanagnosia is attributable to an impairment in the process by which activated structural descriptions are linked to information coding the location of the object.

Directional hypokinesia and hemispatial inattention in neglect.

Subjects with neglect of left hemispace may err to the right when bisecting lines. This error has been attributed either to a directional hypokinesia (failure to execute movements fully in or towards the contralateral hemispace) or to a failure to attend to or represent sensory information. Four subjects with neglect were tested on a line bisection task in which these two hypotheses were differentiated by preventing direct viewing of the line and instead using a video camera and monitor, each of which could be moved independently into right or left hemispace. The performance of 2 subjects was consistent with the predictions of the directional hypokinesia hypothesis; the performance of the other 2 subjects was consistent with the attention-representation deficit hypothesis. These data suggest that both a directional hypokinesia and an attention-representation deficit may each be a primary determinant of neglect.

Preserved object recognition and reading comprehension in optic aphasia.

Optic aphasia is characterized by the ability to name from description and palpation but an inability to name visually-presented objects. Although originally attributed to a disconnection of visual information from object names, optic aphasia is often considered to be a mild form of visual agnosia. We describe a patient with optic aphasia who could access semantic information relevant to objects he could not name and comprehend written words he could not read. These data suggest that, at least in certain cases, this visual modality-specific naming impairment may not be attributable to impaired visual recognition. We suggest that this patient's preserved object recognition and reading comprehension was mediated by a semantic system supported by the right hemisphere.

Prolonged, progressive dementia with spongiform encephalopathy: a variant of Creutzfeldt-Jakob disease?

A 46-year-old female is described with prolonged, progressive dementia and a brain biopsy consistent with Creutzfeldt-Jakob disease (CJD). She had neither myoclonic jerks nor an electroencephalogram with periodic spikes and suppression. Five of her close relatives were also demented. The nosology of CJD was discussed in the light of this case in which histopathology was characteristic of spongiform encephalopathy but the clinical features were atypical. We concluded that it would be premature to expand the traditional diagnostic criteria to include such cases as having CJD but, at the same time, it would be prudent to handle tissue, linens and surgical instruments as if they were contaminated by the resistant agent of CJD.