Induced Microgyria and Auditory Temporal Processing in Rats: A Model for Language Impairment?

Abstract

Studies have shown the existence of minor developmental cortical malformations, including microgyria, in the brains of dyslexics. Concomitant studies have shown that language-impaired individuals exhibit severe deficits in the discrimination of rapidly presented auditory stimuli, including phonological and nonverbal stimuli (i.e., sequential tones). In an effort to relate these results, male rats with neonatally induced microgyria were tested in an operant paradigm for auditory discrimination of stimuli consisting of two sequential tones. Subjects were shaped to perform a go/no-go target identification, using water reinforcement. Stimuli were reduced in duration from 540 to 249 msec across 24 d of testing. Results showed that all subjects were able to discriminate at longer stimulus durations. However, bilaterally lesioned subjects showed specific impairment at stimulus durations of 332 msec or less, and were significantly depressed in comparison to shams. Right- and left-lesioned subjects were significantly depressed in comparison to shams at the shortest duration (249 msec). These results suggest a possible link between the neuropathologic anomalies and the auditory temporal processing deficits reported for language-impaired individuals.

Development of structure and function in the infant brain: Implications for cognition, language and social behaviour

“…A focal freezing lesion administered on postnatal day 1 in the rat (when neurons are still migrating in the cortex) results in 4-layered neocortical microgyria, similar to those found in humans with dyslexia (Fitch et al, ,1994. Several investigators have found that rats with induced cerebrocortical microgyria are impaired on rapid auditory processing tasks, both as mature animals (Clark et al, 2000Herman et al (1997) and across development Peiffer et al, 2004).…”

“…Processing of rapid, successive auditory stimuli has also been studied in rodents using both electrophysiological and behavioural paradigms (Fitch et al, 1994;Frenkel et al, 2000;Friedman et al 2004;Peiffer et al, 2004). Of course, animal models enable researchers to investigate the effects of induced lesions and malformations in a manner not possible with humans.…”

Global versus local processing of frequency-modulated tones in gerbils: An animal model of lateralized auditory cortex functions

“…Therefore, some authors concluded that the laterality effect is related to the communicative valence of signals rather than to their acoustic characteristics (36). Studies applying different artificial, semantically neutral sounds, only occasionally performed in animals (Table S1), yielded inconsistent results (34,(37)(38)(39)(40)(41).…”

The notion of ‘phonology’ in dyslexia research: cognitivism—and beyond

“…Miller and Tallal (1996) make this claim: '[W]e believe that we have identified an underlying neurological impairment that disrupts temporal processing rates in the brains of language learning impaired individuals ' (p. 8). Taken together with the suggestion that the problems dyslexics have can be traced back to anomalies in the magnocellular system (Livingstone, Rosen, Drislane & Galaburda, 1991;Galaburda, Menard, & Rosen, 1994;Fitch, Tallal, Brown, Galaburda, & Rosen, 1994), we discern the following implicit chain of causes in Tallal's and her colleagues' reasoning: (1) Neurological impairment leading to (2) anomalies in temporal processing leading to (3) auditive anomalies leading to (4) phonological anomalies leading to (5) language and cognitive problems. As we see their work, only the first link in this chain, the neurological impairment, is purely biological.…”