In my post from January, I mentioned a surprising finding in a study by Chang et al. (2018): They investigated intrinsic connectivity networks in children who do and do not stutter and found, among others, anomalous, mainly reduced functional connectivity within the visual network (VN) and even more reduced connectivity between VN and dorsal attention network as well as between VN and default mode network in children who stutter, as compared with their normal fluent peers (see Fig. 4 in the study). I took this finding as indicating a general deficit in the involvement of sensory input in the control of behavior. .
This view seems now to be confirmed by the results of a study from Finland, published online this week, by Johanna Piispala, Tuomo Stark, Eira Jansson-Verkasalo, and Mika Kallio: “Decreasedoccipital alpha oscillation in children who stutter during a visualGo/Nogo task.”
I still read only the Abstract which however provides sufficient information for our purpose. The researchers investigated the main oscillations of the brain in 7-9 year old children who stutter and and in age-matched typically developed children in order to discover potential differences related to attention and inhibitory control. EEG data were collected during a visual Go/Nogo task. Stuttering children showed reduced inhibition of the visual cortex and information processing in the absence of visual stimuli, which, so the authors conclude, “may be related to problems in attentional gating. […] Our findings support the view of stuttering as part of a wide-ranging brain dysfunction most likely involving also attentional and inhibitory networks.”
So much about the paper by Piispala and colleagues. The Attention Allocation Theory of stuttering proposed in my website describes a potential relation between attention regulation and a pathomechanism of stuttering, which can be summarized in the causal chain depicted below (it’s the same figure as in my website, but with some explanations).
The causal chain can be closed to a vicious cycle when a child, after having experienced many instances of stuttering, begins to expect this trouble whenever he or she starts talking: Expectation of stuttering, anticipatory struggle, and fear then strongly contribute to the misallocation of attention that has caused the disorder. ‘Disrupted feedback’ in the figure below means that sensory, mainly auditory feedback is not sufficiently processed, not completely transmitted or cached.
For a long time I believed that this vicious cycle is the way in which stuttering becomes persistent, but this is probably not correct: In an diffusion tensor imaging study, Chow and Chang (2017) found differences in the brain between children who eventually recovered from stuttering and those who persisted (see my post from January). These differences were already present in very young children, thus they can hardly be consequences of stuttering. So I now assume that persistence or recovery are predetermined in most cases, either genetically or by early brain development prior to the onset of childhood stuttering.
The ‘vicious cycle’ might nevertheless exist, but influencing only the severity of stuttering including secondary behaviors. Getting out of that cycle, e.g., by desensitization might therefore be the first step of successful therapy.