Table 4. Spearman-Brown rank correlations between N_e/ERN amplitudes and clinical/psychological characteristics in patients with Parkinson’s disease (PD) and healthy controls (HC).

	HC (N = 13)		PD (N = 13)
	off	on	off	on
disease duration	—	—	0.609*	0.160
LEDD	—	—	0.220	0.148
age	0.105	0.074	0.609*	0.412
education	−0.055	0.114	−0.391	−0.173
cognitive status (MoCA)	−0.495	−0.225	−0.155	−0.293
apathy (AES)	−0.207	−0.190	0.675*	0.694**
depression (BDI-II)	−0.504	−0.342	0.623*	0.421
psychiatric status (BSI-18)	−0.243	−0.047	0.743**	0.532
health status (SF-36)	0.315	−0.063	−0.764**	−0.409
impulsiveness (BIS-Brief)	0.003	−0.136	0.556*	0.415
functional impulsivity (DII functional)	0.192	0.070	−0.502	−0.161
dysfunctional impulsivity (DII dysfunctional)	−0.114	−0.342	0.469	0.363
impulse control (QUIP-RS)	0.400	0.500	0.573	0.406
impulse control (QUIP-RS impulse control disorder)	0.386	0.463	0.602*	0.384
schizotypal traits (SPQ)	−0.250	0.071	0.631*	0.222

Note. Positive correlations indicate that higher scores on the respective measure are associated with less negative (i.e., smaller) N_e/ERN amplitudes. Negative correlations indicate that higher scores on the respective measure are associated with more negative (i.e., larger) N_e/ERN amplitudes. Bold typeface indicates significant differences of correlation coefficients between PD and HC (p < 0.05). For PD patients, the conditions “off” and “on” indicate the actual medication state (i.e., whether the patients had taken their usual dose of medication [on] or were tested after withdrawal from dopaminergic medication [off]). The HC group was not administered with dopaminergic medication at any time, and the conditions “off” and “on” were merely used to assign control participants to one of two possible orders of medication conditions (see Methods for detailed explanation). LEDD = levodopa equivalent daily dose, calculated using the conversion factors by ref. 24; MoCA = Montreal Cognitive Assessment²²; WST = Wortschatztest²⁷; AES = Apathy Evaluation Scale⁶³; BDI-II = Beck Depression Inventory-II⁶⁴; BSI-18 = Brief Symptom Inventory (18-item version)⁶⁵; SF-36 = Short Form Health Survey⁶⁶; BIS-Brief = Barratt Impulsiveness Scale (8-item version)⁶⁷; DII = Dickman Impulsivity Inventory⁶⁸; QUIP-RS = Questionnaire for Impulsive-Compulsive Disorders in Parkinson’s Disease—Rating Scale⁶⁹; SPQ = Schizotypal Personality Questionnaire⁷⁰.

*p < 0.05, **p < 0.01.