Table 2.

Longitudinal follow-up studies of the effects of DBS on cognition in PD patients

First author, year	Cases (n)	Follow-up duration (year)	Research methods	Targets	Outcomes
Parsons 2006[99]	612	–	Meta-analysis	STN	Small effects on all cognitive domains assessed, declines in the executive, and memory domain were statistically significant
Appleby 2007[100]	10,339	–	Meta-analysis	–	57% studies examining cognitive outcomes showed no cognitive change and 31% reported improvement
Lhommée 2012[15]	63	1	Multicenter	STN	Cognitive evaluation unchanged
			Prospective
Williams 2010[101]	366	1	Randomized	Bilateral STN	General cognitive function after DBS compared with a medically treated control group remained unchanged
			Open-label
			Prospective
			Multicenter
			Medicine control
Pillon 2000[102]	56	1	Prospective	Bilateral STN	STN patients had no cognitive deficit, except for lexical fluency
Krack 2003[43]	49	5	Prospective	Bilateral STN	Average scores for cognitive performance remained unchanged
Fasano 2010[89]	20	8	Prospective	Bilateral STN	Mild cognitive decline did not have clinical meaning
Rizzone 2014[90]	26	11	Multicenter	Bilateral STN	Global cognitive functions, abstract reasoning, memory and phonological verbal fluency are in the normal range, but phonological verbal fluency remarkable declined
			Prospective
Follett 2010[93]	299	2	Multicenter	152 (GPi)	Secondary outcome: Similarly slight decrements in cognitive function in STN and GPi DBS group
			Randomized	147 (STN)
			Prospective
Odekerken 2013[94]	125	1	Multicenter	62 (GPi)	Primary outcome: No difference between STN and GPi DBS in terms of cognition
			Randomized	63 (STN)
			Prospective
Jiang 2015[3]	10	5	Prospective	Bilateral STN	Mostly unchanged by self-comparison

PD: Parkinson’s disease; DBS: Deep brain stimulation; STN: Subthalamic nucleus; GPi: Globus pallidus internus.