Andrea M. Loftus

Different mechanisms contributing to savings and anterograde interference are impaired in Parkinson's disease.

Reinforcement and use-dependent plasticity mechanisms have been proposed to be involved in both savings and anterograde interference in adaptation to a visuomotor rotation (cf. Huang et al., 2011). In Parkinsons disease (PD), dopamine dysfunction is known to impair reinforcement mechanisms, and could also affect use-dependent plasticity. Here, we assessed savings and anterograde interference in PD with an A1-B-A2 paradigm in which movement repetition was (1) favored by the use of a single-target, and (2) manipulated through the amount of initial training. PD patients and controls completed either limited or extended training in A1 where they adapted movement to a 30° counter-clockwise rotation of visual feedback of the movement trajectory, and then adapted to a 30° clockwise rotation in B. After subsequent washout, participants readapted to the first 30° counter-clockwise rotation in A2. Controls showed significant anterograde interference from A1 to B only after extended training, and significant A1-B-A2 savings after both limited and extended training. However, despite similar A1 adaptation to controls, PD patients showed neither anterograde interference nor savings. That extended training was necessary in controls to elicit anterograde interference but not savings suggests that savings and anterograde interference do not result from equal contributions of the same underlying mechanism(s). It is suggested that use-dependent plasticity mechanisms contributes to anterograde interference but not to savings, while reinforcement mechanisms contribute to both. As both savings and anterograde interference were impaired in PD, dopamine dysfunction in PD might impair both reinforcement and use-dependent plasticity mechanisms during adaptation to a visuomotor rotation.

Exercise and Parkinson's: benefits for cognition and quality of life

Cruise KE, Bucks RS, Loftus AM, Newton RU, Pegoraro R, Thomas MG. Exercise and Parkinson’s: benefits for cognition and quality of life.
Acta Neurol Scand: 2011: 123: 13–19.
© 2010 The Authors Journal compilation

Prism adaptation overcomes pseudoneglect for the greyscales task

Visuomotor adaptation to left-shifting prisms can affect performance for a variety of tasks in neurologically intact (normal) participants. This study examined whether visuomotor adaptation affects performance on the greyscales task in normal participants. Forty-two normal participants completed a greyscales task before and after adaptation to either: left-shifting prisms, right-shifting prisms or control spectacles that did not shift the visual scene. Participants demonstrated a leftward bias (i.e., selected the stimulus that was darker on the left as being darker overall) that was reversed by a short period of visuomotor adaptation to left-shifting prisms. In contrast, this bias was unaffected by adaptation to right-shifting prisms and control spectacles. The findings demonstrate that a simple visuomotor task can alter the distribution of spatial attention for the greyscales task in normal participants.

Pseudoneglect for the bisection of mental number lines

Patients with unilateral neglect of the left side bisect physical lines to the right whereas individuals with an intact brain bisect lines slightly to the left (pseudoneglect). Similarly, for mental number lines, which are arranged in a left-to-right ascending sequence, neglect patients bisect to the right. This study determined whether individuals with an intact brain show pseudoneglect for mental number lines. In Experiment 1, participants were presented with visual number triplets (e.g., 16, 36, 55) and determined whether the numerical distance was greater on the left or right side of the inner number. Despite changing the spatial configuration of the stimuli, or their temporal order, the numerical length on the left was consistently overestimated. The fact that the bias was unaffected by physical stimulus changes demonstrates that the bias is based on a mental representation. The leftward bias was also observed for sets of negative numbers (Experiment 2)—demonstrating not only that the number line extends into negative space but also that the bias is not the result of an arithmetic distortion caused by logarithmic scaling. The leftward bias could be caused by a rounding-down effect. Using numbers that were prone to large or small rounding-down errors, Experiment 3 showed no effect of rounding down. The task demands were changed in Experiment 4 so that participants determined whether the inner number was the true arithmetic centre or not. Participants mistook inner numbers shifted to the left to be the true numerical centre—reflecting leftward overestimation. The task was applied to 3 patients with right parietal damage with severe, moderate, or no spatial neglect (Experiment 5). A rightward bias was observed, which depended on the severity of neglect symptoms. Together, the data demonstrate a reliable and robust leftward bias for mental number line bisection, which reverses in clinical neglect. The bias mirrors pseudoneglect for physical lines and most likely reflects an expansion of the space occupied by lower numbers on the left side of the line and a contraction of space for higher numbers located on the right.

Look, no hands: A perceptual task shows that number magnitude induces shifts of attention

The mental representation of numbers along a line oriented left to right affects spatial cognition, facilitating responses in the ipsilateral hemispace (the spatial-numerical association of response codes [SNARC] effect). We investigated whether the number/space association is the result of an attentional shift or response selection. Previous research has often introduced covert left/right response cues by presenting targets to the left or the right. The present study avoided left/right cues by requiring forced choice upper/lower luminance discriminations to two mirror-reversed luminance gradients (the grayscale task). The grayscale stimuli were overlaid with strings of (1) low numbers, (2) high numbers, and (3) nonnumerical characters. In Experiment 1, 20 dextrals judged the number’s magnitude and then indicated whether the upper/lower grayscale was darker. Results showed leftward and rightward attentional biases for low and high numbers, respectively. Demands to process numbers along a left/right line were made less explicit in Experiment 2 (N=8 dextrals), using (1) a parity judgment and (2) arbitrary linguistic labels for top/bottom. Once again, a spatial congruency effect was observed. Because the response (up/down) was orthogonal to the dimension of interest (left/right), the effect of number cannot be attributed to late-stage response congruencies. This study required unspeeded responses to stimuli presented in free vision, whereas other experiments have used speeded responses. Understanding the time course of number-space effects may, therefore, be important to the debate associated with response selection.

Short-interval intracortical inhibition and manual dexterity in healthy aging

Short-interval intracortical inhibition (SICI) acting on the first dorsal interosseus was measured using paired-pulse transcranial magnetic stimulation (interstimulus interval=2ms) in samples of young and healthy older subjects and correlated with manual dexterity measured with the Purdue Pegboard test and two isometric force-matching tasks. There was an age-related decrease in SICI and an age-related decline in all dexterity measures. The level of SICI was not correlated with any of the dexterity measures, but the appearance of atypical facilitation (rather than inhibition) in some subjects was associated with impaired pegboard performance but not force-matching performance. We conclude that SICI at rest is reduced with healthy aging but this loss of SICI does not directly contribute to the loss of dexterity; a shift in the balance of facilitatory and inhibitory processes in motor cortex to facilitation might interfere with sequenced hand movements.

A new means of measuring index/ring finger (2D:4D) ratio and its association with gender and hand preference

Relative finger length can predict a persons gender or their hand preference. We measured finger length using a new “tubes” test, which required participants to slide a clear plastic tube over their fingers and read the length from an attached mm scale. Data collected from 600 students demonstrated that the right fingers are longer than the left for dextrals, but not for non-dextrals. Examination of the relative length of the index and ring fingers revealed a clear gender effect. There was also an effect of hand preference on index/ring finger ratio whereby non-dextrals showed a more masculine pattern compared to dextrals. For non-dextrals, prenatal exposure to high testosterone levels may have caused both a shift away from dextrality and a more masculine pattern of finger ratio. In the second experiment, finger length was measured by the tubes test and by photocopying the hands in 124 undergraduates. The tubes test yielded a longer estimate of ring finger length compared to the photocopy method. Despite this, there was a strong correlation between the tests and both showed an association with gender. Finally, test–retest scores for 45 participants showed a high level of reliability for absolute and relative finger measures. We conclude that the tubes technique provides an effective and easy-to-use means of measuring finger length, which can be administered in a classroom setting.

Coping processes and health‐related quality of life in Parkinson's disease

This study investigated the predictive value of various coping processes for the psychological and disease specific aspects of health‐related quality of life (HRQoL) in Parkinsons disease (PD).

Pseudoneglect and neglect for mental alphabet lines

While patients with right parietal damage neglect the left side of stimuli, the intact-brain population shows a slight neglect of the right side--known as pseudoneglect. Although pseudoneglect occurs for physical stimuli, it is not certain whether the bias extends to mental representations. To investigate this issue, we examined spatial distortions in the representation of length for mental alphabet lines, which are thought to have a left-to-right arrangement. In Expt. 1, participants (n=10) were presented with letter strings (e.g. C_H_P) and estimated whether the letter length was greater on the left or right side of the inner-letter. The strings were presented simultaneously along a line or sequentially in the centre of the screen in either an ascending (i.e. A-Z) or descending (i.e. Z-A) sequence. Participants reliably overestimated the length on the left regardless of presentation mode. In Expt. 2, participants (n=20) judged whether the inner-letter was the true centre. Responses were biased such that inner-letters shifted to the left of true centre were perceived to be the centre. Combined, both studies demonstrate that the length on left side of the mental alphabet line is overestimated relative to the right. In Expt. 3, a reversal of the bias towards the right was found for a group of neglect patients. The data demonstrate that letters have a left-to-right mental representation and that the left side of this representation is overrepresented in a manner similar to the overestimation associated with pseudoneglect for physical stimuli.

Testing the activation-orientation account of spatial attentional asymmetries using transcranial direct current stimulation

The general population shows an attentional bias to the left, known as pseudoneglect. This bias is thought to be driven by higher levels of activation in right parietal areas. Using transcranial direct current stimulation (tDCS) to manipulate activation, this study examined whether tDCS over the left and right posterior parietal cortices (PPC) affects pseudoneglect. Normal participants received tDCS over the left or right PPCs (15 in each group). Pseudoneglect was measured using the greyscales task, which requires a forced-choice discrimination of luminance between two opposing luminance gradients. The greyscales task was administered both before and after; (a) anodal (b) cathodal and (c) sham tDCS. Participants who received tDCS over the left PPC demonstrated pseudoneglect for the greyscales task, which was significantly reduced by anodal tDCS, but was unaffected by sham or cathodal tDCS. In contrast, for those participants who received right PPC tDCS, pseudoneglect for the greyscales task was unaffected by tDCS. Anodal tDCS, which is known to elevate neural excitation, may have overcome lower levels of activation in the left PPC, resulting in decreased pseudoneglect. These findings provide convincing evidence in support of an activation-orientation model of pseudoneglect and have implications for models of left neglect.