Thalamic deep brain stimulation decelerates automatic lexical activation.
Deep Brain Stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) is a therapeutic option for patients with essential tremor. Despite a generally low risk of side effects, declines in verbal fluency (VF) have previously been reported.



We aimed to specify effects of VIM-DBS on major cognitive operations needed for VF task performance, represented by clusters and switches. Clusters are word production spurts, thought to arise from automatic activation of associated information pertaining to a given lexical field. Switches are slow word-to-word transitions, presumed to indicate controlled operations for stepping from one lexical field to another.



Thirteen essential tremor patients with VIM-DBS performed verbal fluency tasks in their VIM-DBS ON and OFF conditions. Clusters and switches were formally defined by mathematical criteria. All results were compared to those of fifteen healthy control subjects, and significant OFF-ON-change scores were correlated to stimulation parameters.



Patients produced fewer words than healthy controls. DBS ON compared to DBS OFF aggravated this deficit by prolonging the intervals between words within clusters, whereas switches remained unaffected. This stimulation effect correlated with more anterior electrode positions.



VIM-DBS seems to influence word output dynamics during verbal fluency tasks on the level of word clustering. This suggests a perturbation of automatic lexical co-activation by thalamic stimulation, particularly if delivered relatively anteriorly. The findings are discussed in the context of the hypothesized role of the thalamus in lexical processing.
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor and Cognition Group, Campus Benjamin Franklin (CBF), Hindenburgdamm 30, 12000 Berlin, Germany.
Felicitas
F
Ehlen
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor and Cognition Group, Campus Benjamin Franklin (CBF), Hindenburgdamm 30, 12000 Berlin, Germany.
Isabelle
I
Vonberg
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor and Cognition Group, Campus Benjamin Franklin (CBF), Hindenburgdamm 30, 12000 Berlin, Germany.
Hannes O
HO
Tiedt
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor Neuroscience Group, Campus Virchow-Klinikum (CVK), Augustenburger Platz 1, 13353 Berlin, Germany; Laboratory for Brain Network Imaging and Modulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
Andreas
A
Horn
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor and Cognition Group, Campus Benjamin Franklin (CBF), Hindenburgdamm 30, 12000 Berlin, Germany.
Ortwin
O
Fromm
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor Neuroscience Group, Campus Virchow-Klinikum (CVK), Augustenburger Platz 1, 13353 Berlin, Germany.
Andrea A
AA
Kühn
Charité - Universitätsmedizin Berlin, Department of Neurology, Motor and Cognition Group, Campus Benjamin Franklin (CBF), Hindenburgdamm 30, 12000 Berlin, Germany. Electronic address: fabian.klostermann@charite.de.
Fabian
F
Klostermann
D000368:Aged; D046690:Deep Brain Stimulation / Q000379:methods*; D020329:Essential Tremor / Q000628:therapy*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D013060:Speech / Q000502:physiology; D020651:Ventral Thalamic Nuclei / Q000502:physiology* / Q000503:physiopathology
Lexical access; Thalamic DBS; Verbal fluency