Fear-conditioned alterations of motor cortex excitability: The role of amygdala

•Responses of corticospinal pathways are potentiated after fear in healthy humans.•Fear-potentiation of reticulospinal and corticospinal pathways are maintained even after resection of unilateral amygdala.•Potentiation of MEPs are maintained even regardless of operation side. We hypothesized that fear-conditioning may increase motor cortical excitability in preparation for response to fear. We tested our hypothesis in healthy subjects and in the second step, to determine the role of amygdala in alterations of motor cortex excitability, we included a group of patients who previously underwent unilateral amygdalo-hippocampectomy for temporal lobe epilepsy. In the first step, we included 16 healthy volunteers. In the second step, 14 patients who previously underwent unilateral amygdalo-hippocampectomy for temporal lobe epilepsy and who were seizure-free were included in the study. Motor evoked potentials (MEPs) recorded over right hand were recorded twice before and after the observation of fearful faces (fear-conditioning). Auditory startle response (ASR) was also recorded. Comparisons of before and after fear-conditioning MEP parameters within the healthy subjects group showed MEP amplitude was higher after fear-conditioning (p=0.019). Same comparison in patients with unilateral amygdalo-hippocampectomy demonstrated shorter MEP latency (p=0.036) and higher MEP amplitudes after fear-conditioning (p=0.046). CSPs did not show any change after this paradigm in both groups. Comparisons of ASR findings before and after fear-conditioning demonstrated enhanced responses after fear-conditioning in both healthy subjects and in patients with unilateral amygdalo-hippocampectomy. For MEPs or ASRs, there was a similar enhancement in patients with left- or right-sided operation. Fear-potentiation of both corticospinal and reticulospinal pathways occurs in healthy humans and bilateral potentiation of ASR and potentiation of MEPs are maintained even after resection of unilateral amygdala regardless of its side.