Brain Modulation and Speech Motor Control

Who we are

We are an interdisciplinary research group of Neurologists and Phoneticians in Cologne investigating the effect of brain modulation on speech motor control in movement disorders. Our special focus is currently on Deep Brain Stimulation (DBS) on patients with Essential Tremor, a rhythmic tremor typically affecting the upper limbs, trunk and voice.

DBS involves electrical stimulation of deep structures in the brain involved in movement control. In Essential Tremor patients, stimulation is applied in the thalamic region (Ventral Intermediate Nucleus, VIM). This stimulation reduces tremor but can lead in some patients to side effects such as slurring of speech, impacting their quality of life.

Our research combines tremor analysis, details as to electrode location and estimation of the volume of tissue activation with detailed auditory and acoustic analysis of the speech signal. We are currently planning a more fine-grained analysis of temporal and spatial aspects of Speech Motor Control using methods for directly capturing movements of the lips and tongue, calculating the speed and direction of the articulators, as well as the coordination between them necessary for producing clear speech.

Our main aims are:

To characterise the side-effects of DBS involving speech motor control

Effects on speech production are typically described as relating to the voice itself (glottal control) or the articulation of the lips, tongue and jaw (supraglottal control). However, not all articulators are affected in the same way and to the same extent, such that e.g. lips and tongue might be affected in different ways.

To identify the causes of these side-effects

The exact location of the DBS electrodes and the amount of current they emit (volume of tissue activation) will be correlated with the speech motor parameters identified using acoustic and articulographic recordings. This research will also contribute towards establishing whether the side effects are due to the target area itself or due to collateral effects on neighbouring regions. Results will contribute further to our understanding of the occurrence of this side effect according to anatomic topology

Relate the occurrence of this side effect

To optimise electrode location and stimulation parameters

– To identify regions within the target area for electrode placement that reduce the likelihood of side effects involving the speech motor system. Results will be used to develop procedures for optimising stimulation settings in general and for each patient individually.

To estimate the individual risk of these side-effects pre-operatively

– With knowledge gained from our research we plan to  develop objective measures based on acoustic analysis for estimating – for each patient – the risk of post-operative speech motor problems when stimulation is applied.