The occasional "independence" of dyslexia and dysgraphia from dysphasia

Cognitive, linguistic and affective disturbances following a right superior cerebellar artery infarction: a case study

The cerebellar cognitive affective syndrome (CCAS) is a neurobehavioral syndrome that may develop after congenital and acquired cerebellar lesions. The syndrome consists of deficits in executive functioning, spatial cognition, visual-spatial memory and language and also involves personality and behavioral changes. We describe a 58-year-old right-handed man who in addition to affective disturbances presented with a unique combination of cognitive and linguistic deficits following an ischemic infarction in the vascular territory of the right superior cerebellar artery (SCA). Neurocognitive and neurolinguistic examinations were performed in the acute phase (10 days post-onset) and lesion phase (four weeks post-onset) of the stroke. A Tc-99m-ECD SPECT study was performed five weeks after the stroke. Acute phase data revealed a generalized cognitive decline and mild transcortical sensory aphasia. In the lesion phase, the neurobehavioral tableau was dominated by executive dysfunctions, disrupted divided attention, disturbed visual-spatial organization and behavioral abnormalities. Neurolinguistic investigations disclosed visual dyslexia and surface dysgraphia. Reading of words and visual lexical decision tasks of words and nonwords were severely defective and predominantly characterized by visual errors. In addition, writing irregular and ambiguous words resulted in regularization errors (phonologically plausible errors based on phoneme-grapheme correspondence rules). In the absence of any structural damage in the supratentorial brain regions, a quantified SPECT study showed a relative hypoperfusion in the right cerebellar hemisphere and the left medial frontal lobe. CCAS is for the first time reported in association with visual dyslexia and surface dysgraphia. We hypothesize that the cognitive and linguistic deficits might result from functional disruption of the cerebellar-encephalic pathways, connecting the cerebellum to the frontal supratentorial areas which subserve attentional and planning processes. This phenomenon of crossed cerebellar-cerebral diaschisis is supported by SPECT findings revealing a hypoperfusion in the anatomoclinically suspected brain regions. The constellation of cognitive, linguistic and behavioral symptoms adds new evidence to the multifaceted area of cerebellar neurocognition and demonstrates that the cerebellum might play a crucial role in cognitive, linguistic, and affective processing.

Does letter-by-letter reading involve the spelling system?

Warrington and Shallice (Brain 103, 99-112, 1980) proposed that letter-by-letter readers can no longer access the visual word-form system, and read by using the spelling system 'in reverse'. Contrary to their suggestion, this paper presents the case of a letter-by-letter reader who appears to use quite different strategies in word reading and spelling. Reading and spelling are both impaired, but they appear to be impaired in different ways. Most strikingly, the patient's spelling errors consist largely of phonological regularizations--indeed there is little evidence that he has any lexical spelling knowledge available--whereas there are virtually no regularizations amongst his reading errors. These are largely visual paralexias and letter misidentifications. It is suggested that this pattern is more easily explained in terms of compensatory mechanisms that access the reading lexicon than by use of the spelling system 'in reverse'.

THE EFFECTS OF CEREBRAL LESIONS ON INTELLECTUAL FUNCTION: A REVIEW OF CURRENT RESEARCH TRENDS

The literature of the psychological effects of brain injury is extensive and disconnected. It abounds in inadequate definitions, incompatible theories and disagreements as to appropriate methods of investigation. This situation results partly from the variety of disciplines which guide different investigators; but it results too from the great logical difficulties encountered by anybody who seeks to throw light on normal intelligent behaviour by studying the effects of cerebral lesions. Some have even argued that such attempts are always unprofitable (47, 77).