title: Decay of motor memories in the absence of error.
abstract: When motor commands are accompanied by an unexpected outcome, the resulting error induces changes in subsequent commands. However, when errors are artificially eliminated, changes in motor commands are not sustained but show decay. Why does the adaptation-induced change in motor output decay in the absence of error? A prominent idea is that decay reflects the stability of the memory. We show results that challenge this idea and instead suggest that motor output decays because the brain actively disengages a component of the memory. Humans adapted their reaching movements to a perturbation and were then introduced to a long period of trials in which errors were absent (error-clamp). We found that, in some subjects, motor output did not decay at the onset of the error-clamp block but a few trials later. We manipulated the kinematics of movements in the error-clamp block and found that, as movements became more similar to subjects' natural movements in the perturbation block, the lag to decay onset became longer and eventually reached hundreds of trials. Furthermore, when there was decay in the motor output, the endpoint of decay was not zero but a fraction of the motor memory that was last acquired. Therefore, adaptation to a perturbation installed two distinct kinds of memories: (1) one that was disengaged when the brain detected a change in the task and (2) one that persisted despite it. Motor memories showed little decay in the absence of error if the brain was prevented from detecting a change in task conditions.
authors: Department of Neuroscience and Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA. pvaswani@jhmi.edu
authors: Pavan A
authors: PA
authors: Vaswani
authors: Reza
authors: R
authors: Shadmehr
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology; D008297:Male; D008568:Memory / Q000502:physiology*; D015233:Models, Statistical; D009068:Movement / Q000502:physiology*; D011237:Predictive Value of Tests; D011336:Probability; D011597:Psychomotor Performance; D013997:Time Factors; D055815:Young Adult
references: J Neurophysiol. 2007 Jun;97(6):3997-4006
references: 17392418
references: J Neurophysiol. 2010 Jul;104(1):382-90
references: 20484533
references: J Neurosci. 1994 May;14(5 Pt 2):3208-24
references: 8182467
references: J Neurosci. 1997 Jan 1;17(1):409-19
references: 8987766
references: J Neurophysiol. 2008 Nov;100(5):2948-55
references: 18784273
references: J Neurosci. 2011 Jul 6;31(27):10050-9
references: 21734297
references: Neuron. 2011 May 26;70(4):787-801
references: 21609832
references: J Neurophysiol. 2009 Aug;102(2):931-40
references: 19494195
references: J Neurophysiol. 2004 May;91(5):2110-6
references: 14711974
references: Cereb Cortex. 2011 Aug;21(8):1761-70
references: 21139077
references: J Neurosci. 2011 Sep 28;31(39):13829-39
references: 21957245
references: PLoS Comput Biol. 2010 Aug 19;6(8):
references: 20808880
references: J Neurophysiol. 2008 May;99(5):2577-83
references: 18353917
references: J Neurophysiol. 2000 Aug;84(2):853-62
references: 10938312
references: J Neurosci. 2010 Nov 3;30(44):14817-23
references: 21048140
references: Neural Comput. 2006 Apr;18(4):760-93
references: 16494690
references: J Neurosci. 2012 Oct 17;32(42):14617-21
references: 23077047
references: J Neurosci. 2008 Sep 24;28(39):9610-8
references: 18815247
references: J Neurosci. 2010 Apr 14;30(15):5159-66
references: 20392938
references: PLoS Biol. 2006 Jun;4(6):e179
references: 16700627
references: J Neurophysiol. 2008 Nov;100(5):2537-48
references: 18596178
references: J Neurosci. 2009 Aug 19;29(33):10396-404
references: 19692614
references: Nat Neurosci. 2007 Jun;10(6):779-86
references: 17496891
references: Nature. 2000 Oct 12;407(6805):742-7
references: 11048720
references: J Neurosci. 2012 Mar 21;32(12):4230-9
references: 22442085
references: J Neurophysiol. 2012 Feb;107(4):1247-56
references: 22157120