Neural correlates of sequence learning in children with developmental dyslexia

Abstract

Developmental Dyslexia (DD) is a condition in which reading accuracy and/or fluency falls substantially below what is expected based on the individuals age, general level of cognitive ability, and educational opportunities. The procedural circuit deficit hypothesis (PDH) proposes that DD may be largely explained in terms of alterations of the cortico-basal ganglia procedural memory system (in particular of the striatum) whereas the (hippocampus-dependent) declarative memory system is intact, and may serve a compensatory role in the condition. The present study was designed to test this hypothesis. Using Magnetic Resonance Imaging, we examined the functional and structural brain correlates of sequence-specific procedural learning (SL) on the serial reaction time task, in 17 children with DD and 18 typically developing (TD) children. The study was performed over 2 days with a 24-h interval between sessions. In line with the PDH, the DD group showed less activation of the striatum during the processing of sequential statistical regularities. These alterations predicted the amount of SL at day 2, which in turn explained variance in children's reading fluency. Additionally, reduced hippocampal activation predicted larger SL gains between day 1 and day 2 in the TD group, but not in the DD group. At the structural level, caudate nucleus volume predicted the amount of acquired SL at day 2 in the TD group, but not in the DD group. The findings encourage further research into factors that promote learning in children with DD, including through compensatory mechanisms.

Keywords: developmental dyslexia; hippocampus; procedural memory; sequence learning; statistical learning; striatum.

FIGURE 1

(a) A schematic of the serial reaction time task used in the study. (b) Study design

FIGURE 2

Sequence‐specific learning (SL) across day 1 and day 2 displayed by groups. In order to provide a more fine‐grained view of learning, the data for each day is divided into two runs with each run consisting of 12 blocks

FIGURE 3

Brain activation associated with sequence‐specific learning (SL). Results are displayed at a corrected threshold of p ^FWE < .05. All results are reported in MNI space. Activation is shown on transverse sections of the brain

FIGURE 4

(a) A significant positive association between sequence‐specific (sequence > random) BOLD‐signal on day 2 and behavioral sequence‐specific learning day 2 (SL day 2) in left CN [x, y, z = ‐20, 10, 12] was found across all participants as well as within the DD group. (b) A significant positive association between sequence‐specific (sequence > random) BOLD signal on day 2 and behavioral sequence‐specific learning day 2 (SL day 2) was found in left CN across all participants as well as within the DD group for anatomically defined ROIs. (c) A significant positive association between sequence‐specific (sequence > random) BOLD signal on day 2 and behavioral sequence‐specific learning day 2 (SL day 2) was also found in the right CN across all participants as well as within the DD group for anatomically defined ROIs (d) Activation in the right CN for sequence‐specific learning (SL) across day 1 and day 2 for TD and DD children. DD children had significantly less activation compared to the TD children as indicated by the group by day interaction

FIGURE 5

Associations between sequence‐specific BOLD‐signal on day 2 and sequence‐specific learning day 2 (SL day 2) in the anatomically defined ROIs of left and right HC. A significant negative association was demonstrated in the TD group but not in the DD group

FIGURE 6

(a) GM volume of the HC, CN, and putamen in DD children and TD children. Children in the DD group had on average lower GM volume in the left CN compared with TD children. (b) Significant positive associations between GM volume of the left (top) and right (bottom) CN and sequence‐specific learning day 2 (SL day 2) was found within the TD group but not in the DD group. (c) A significant positive association between GM volume in the left CN and change in sequence‐specific learning between day 1 and day 2 (SL change) was found in the TD group but not in the DD group (top). A significant positive association between GM volume in the right HC and change in sequence‐specific learning between day 1 and day 2 (SL change) was found in the DD group but not in the TD group (bottom)

FIGURE 7

The link between striatal sequence‐specific brain activity, sequence‐specific learning (SL), and reading fluency