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GABA involvement was studied in 23 TS children, aged 8-12, and 67 controls using a battery of vibrotactile tasks with a subset also undergoing GABA-edited magnetic resonance spectroscopy \citep{26041822}. Lower GABA concentrations in the right sensorimotor cortex was associated with greater motor tic severity (r=-0.55). There were no significant differences between groups on reaction time and baseline amplitude discrimination threshold. Control children showed the expected increase in discrimination threshold after being exposed to a dynamically increasing subthreshold stimulus while TS children did not. The authors suggest that this is related to abnormal GABAergic inhibition although they point out that larger studies are needed to determine to what extent the high proportion of TS subjects with ADHD influenced the results.   A detailed review discusses histaminergic modulation of striatal function by the tuberomamillary nucleus of the hypothalamus \cite{26275849}. \citep{26275849}.  Histamine suppresses both the thalamic and cortical drive to medium-spiny projection neurons (MSNs), modulates thalamostriatal synapses resulting in a facilitation of thalamic input, and suppresses lateral feedback inhibition. The authors suggest that during wakefulness and increased attention the striatum will be more responsive to thalamostriatal input and feed-forward inhibition will predominate. The role of histamine in TS was discussed in terms of a rare mutation involving histamine synthesizing enzyme histidine decarboxylase in one TS human adult, decreased pre-pulse inhibition of startle responses, and in a rodent model an increase in a variety of amphetamine-induced stereotypies which decreased in response to histamine infusion or use of haloperidol. These effects were thought to occur as a result of the histaminergic control of the lateral GABAergic inhibitory connections between MSNs. The authors also discussed ongoing research on histaminergic treatments for TS. ### Clinical and neuropsychological studies