Ahissar, M. | bioRxiv Science

bioRxiv2017

Widespread shorter cortical adaptation in dyslexia

Studies of dyslexics performance on perceptual tasks suggest that their implicit inference of sound statistics is impaired. In a previous paper (Jaffe-Dax, Frenkel, & Ahissar, 2017), using 2-tone frequency discrimination, we found that the effect of previous trial frequencies on dyslexics judgments decayed faster than the effect on controls judgments, and that the adaptation of their ERP responses to tones recovered faster. Here, we show the cortical distribution of this abnormal dynamics of adaptation using fast acquisition fMRI. We find that dyslexics faster decay of adaptation is widespread, though the most significant effects are found in the left superior temporal lobe, including the auditory cortex. This broad distribution suggests that dyslexics faster decay of implicit memory is a general characteristic of their cortical dynamics, which also encompasses the sensory cortices.

neuroscience↗

bioRxiv2016

Shorter neural adaptation to sounds accounts for dyslexics’ abnormal perceptual and reading dynamics

Dyslexia is a prevalent reading disability whose underlying mechanisms are still disputed. We studied the neural mechanisms underlying dyslexia using a simple frequency-discrimination task. Though participants were asked to compare the 2-tones in each trial, implicit memory of previous trials affected their responses. We hypothesized that implicit memory decays faster among dyslexics. We tested this by increasing the temporal intervals between consecutive trials, and measuring the behavioral impact and ERP responses from the auditory cortex. Dyslexics showed a faster decay of implicit memory effects on both measures, with similar time constants. Finally, faster decay also characterized dyslexics benefits in oral reading rate. It decreased faster as a function of the time interval from the previous reading of the same non-word. We propose that dyslexics shorter neural adaptation paradoxically accounts for their longer reading times, since it induces noisier and less reliable predictions for both simple and complex stimuli.

neuroscience↗