Objective: In present study, we investigated the impact of temporal discrimination threshold (TDT) prolongation on simple repetitive finger tapping and dexterous finger movement in patients with Parkinson’s disease (PD).

Background: Accurate sensory information is essential for precise control of movement. Parkinson’s disease (PD) patients often exhibit various forms of higher-order sensory dysfunctions including temporal discrimination threshold (TDT) prolongation. However, the impact of prolonged TDT on Parkinsonian motor deficits has not previously been investigated in detail.

Methods: In the present study, 33 PD patients and 24 age- and gender- matched controls underwent assessments for the degree of finger movement impairment using (i) the Unified Parkinson’s disease Rating Scale (UPDRS) for finger movement (summation of UPDRS Items 23 and 24), (ii) an inertial sensor, and (iii) a coin rotation task (CRT). Using the inertial sensor, we measured the speed, amplitude, and frequency of finger tapping. We investigated the impact of prolonged index finger TDT on the finger movements of these patients using a linear mixed model.

Results: In comparison to the control group, CRT performance by PD patients was significantly worse (PD vs. control; left side = 9.89 ± 3.47 vs.13.83 ± 2.68; right side = 10.76 ± 3.35 vs. 14.46 ± 3.49; p < 0.001). Kinematic parameters of finger tapping for PD and control groups are summarized in Table 1.

Comparison of kinematic parameters of finger tapping between PD and control groups

	Left side		Right side		p-values
	Control	PD	Control	PD
Mean amplitude	86.70 ± 24.45	72.23 ± 21.15	83.24 ± 17.42	64.39 ± 22.48	0.005**
Mean speed	529.36 ± 164.73	393.98 ± 155.46	496.93 ± 104.46	347.47 ± 130.62	< 0.001**
Mean frequency	3.05 ± 0.32	2.77 ± 0.62	3.04 ± 0.55	2.85 ± 0.73	0.062
Amplitude slope	-0.08 ± 0.26	-0.38 ± 0.45	-0.14 ± 0.50	-0.31 ± 0.36	0.019*
Speed slope	-1.51 ± 1.67	-2.20 ± 2.13	-0.77 ± 2.10	-1.63 ± 2.01	0.046*
Frequency slope	-0.01 ± 0.01	0.00 ± 0.01	0.00 ± 0.01	0.00 ± 0.02	0.510
Amplitude % CoV	10.96 ± 4.94	18.71 ± 8.66	12.09 ± 6.02	17.10 ± 9.25	0.002**
Speed % CoV	11.44 ± 4.14	19.25 ± 8.44	11.14 ± 5.04	17.14 ± 9.17	< 0.001**
Frequency & CoV	7.46 ± 2.84	18.86 ± 19.57	7.35 ± 3.11	15.26 ± 15.22	0.014*

CoV, coefficient of variance; p = obtained from repeated measure analysis of covariance, corrected for multiple testing by Benjamini-Hochberg correction; * = p < 0.05; ** = p < 0.01” In comparison to healthy controls, TDT was found to be prolonged in PD patients. There was no impact of TDT on mean values and decrement for amplitude and speed, as well as mean values, decrement and variability of tapping frequency. However, prolonged TDT had a significant impact on the variability in amplitude (estimate = 8.104 × 10-4, p = 0.03) and speed (estimate = 7.790 × 10-4, p = 0.03). Although prolonged TDT had no significant impact on UPDRS scores for finger movement, it correlated with poorer performance on the CRT (estimate = -2.689 × 10-2; p = 0.015). (Table 2)

Effect of TDT prolongation on finger tapping kinematic parameters in PD patients

Kinematic parameters	Estimate (× 10-4)	SE (× 10-4)	95% CI (× 10-3)	p-values
Mean amplitude	39.713	729.499	-141.853 ∼ 149.796	0.960
Mean speed	-2780.828	4639.571	-1205.520 ∼ 649.354	0.709
Mean frequency	-15.232	21.661	-5.853 ∼ 2.807	0.709
Amplitude slope	-18.698	13.465	-4.561 ∼ 0.822	0.306
Speed slope	-96.746	68.171	-23.302 ∼ 3.953	0.306
Frequency slope	0.024	0.468	-0.091 ∼ 0.096	0.960
Amplitude CoV	8.104	2.812	0.248 ∼ 1.373	0.030*
Speed CoV	7.790	2.777	0.224 ∼ 1.334	0.030*
Frequency CoV	9.106	5.754	-0.240 ∼ 2.061	0.306

TDT = somatosensory temporal discrimination threshold; SE = standard error; CI = confidence interval; p = p-values corrected for multiple testing by Benjamini-Hochberg correction; * = p < 0.05

Conclusions: Cutaneous temporal discriminative sensory dysfunction seen in these PD patients appears to increase variability in the speed and amplitude of fast repetitive finger movements and disturbs finger dexterity.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impact-of-prolonged-temporal-discrimination-threshold-on-finger-movements-of-parkinsons-disease/