Geoff Hammond

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.

Handedness in schizophrenia: a quantitative review of evidence

Objective:  The prevalence of various anomalous handedness subtypes in schizophrenia patients remains ambiguous. Although current literature favours the notion that the shift in lateral preferences seen is because of an increase of mixed‐handedness, several studies suggest that exclusive left handedness is more prevalent than in the general population.

Interpretation revealed in the blink of an eye: Depressive bias in the resolution of ambiguity

Self-report measures of interpretation have been criticized on methodological grounds. An approach is introduced in this article that enables the assessment of interpretive bias with a greater degree of methodological rigor than previously has been the case. Psychophysiological researchers have established that the magnitude of the human blink reflex is augmented when elicited during negative rather than neutral imagery. The 1st experiment demonstrates that the blink reflex is sensitive to the emotional valence of imagery evoked by interpretations imposed on ambiguous stimuli. In the 2nd experiment, this measure is used to assess interpretations imposed on ambiguous stimuli by individuals who differ in depression levels. The findings are consistent with the hypothesis that depression is associated with a negative interpretive bias.

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.

The Objections to Null Hypothesis Testing as a Means of Analysing Psychological Data

The objections which have been made to testing statistical null hypotheses as the means of analysing the results of psychological research are assembled. None of these criticisms is by itself new, and none is controversial. Together, however, these criticisms demand a fundamental change in the way we analyse the results of psychological research and the way in which we teach students to analyse data. In order to cumulate a reliable body of knowledge, psychologists should dispense with statistical hypothesis testing and instead use empirical replication as the test of reliability, and should report effect size measures together with an indication of their likely error.

Anxiety-linked task performance: Dissociating the influence of restricted working memory capacity and increased investment of effort

The present set of studies evaluated two specific predictions generated by Eysenck et al.s (2007) attentional control theory of anxiety-linked task performance. First, to the extent that a task increases the need for working memory capacity, an anxiety-linked performance decrement should become more evident. Second, to the extent that a task increases the likelihood of effort, this anxiety-linked performance decrement should attenuate. Experiments 1 and 2 examined the learning performance of low and high trait anxious participants in capacity-dependent and capacity-independent tasks, under incidental and intentional learning conditions. Experiments 3 and 4 then examined the learning preference of such participants under incidental and intentional learning conditions. The pattern of findings provides direct support for the models predictions.

Schizotypy and mixed-handedness revisited

Although some previous studies assert that an association between schizotypy and loss of hand dominance is well established, the prevailing use of student populations, small effect sizes and arbitrariness of handedness classification suggest that this tentative association merits further investigation. The association of schizotypy and loss of hand dominance was examined using four samples. The first comprised 353 randomly selected individuals from the general community, the second comprised 131 screened volunteers participating as control subjects in a family study of schizophrenia, the third included 97 full siblings of schizophrenia patients, and the fourth consisted of 176 schizophrenia patients from the same study. The samples of screened volunteers and nonpsychotic siblings were used to replicate results from the community sample and to test the hypothesis that an increase in genetic liability is related to the association of schizotypal traits and mixed handedness. The results demonstrated that mixed handedness and schizotypy traits were unrelated in the representative sample from the community. This finding was replicated in the sample of screened volunteers, while siblings of schizophrenia patients showed a trend in the direction of the hypothesised relationship. In contrast, there was an expected significant but low in magnitude association between loss of hand dominance and the Schizotypal Personality Questionnaire factor of Cognitive Perceptual Dysfunction in schizophrenia patients.

Excitability of intracortical inhibitory and facilitatory circuits during ischemic nerve block

PURPOSE The primary motor cortex is capable of rapid, reversible plastic changes and longer-term, more permanent reorganization. Ischemic nerve block (INB) is a model of deafferentation-induced short-term plasticity. We used transcranial magnetic stimulation to examine whether changes in the excitability of short- and/or long-interval intracortical inhibitory (SICI, LICI) or short-interval intracortical facilitatory (SICF) circuits underlie the corticospinal excitability increases observed during INB. METHODS SICI and LICI recruitment curves, obtained by varying conditioning stimulus intensity, and SICF were measured at multiple inter-stimulus intervals (ISIs). RESULTS Forearm flexor MEP amplitude increased during INB at the wrist; this was not accompanied by changes in SICI at ISIs of 1 or 2 ms, in SICF at ISIs of 1.2, 2.7, or 4.4 ms, or in LICI at an ISI of 80 ms, but was accompanied by an increase in LICI at an ISI of 150 ms. CONCLUSIONS The results suggest that (1) the increased excitability of forearm flexors is not due to reduced SICI or LICI or increased SICF, and (2) LICI measured at ISIs of 80 and 150 ms are distinct processes. We discuss the importance of identifying distinct processes of LICI and speculate regarding other mechanisms that could potentially underlie INB-induced plasticity.

Age-related changes in short-interval intracortical facilitation and dexterity

Functional changes in the primary motor cortex might contribute to age-related decline in fine motor control. We measured short-interval intracortical facilitation (SICF) in an intrinsic hand muscle with paired-pulse transcranial magnetic stimulation at interstimulus intervals (ISIs) of 1.5, 2.5, and 4.5 ms in young and old participants and examined its association with dexterity. We found age-related effects in SICF, with greater facilitation in old than young participants at the 1.5-ms ISI and greater facilitation in young than old participants at the 2.5-ms ISI. SICF at the 2.5-ms ISI was positively correlated with performance on a task that required coordinated and dextrous use of both hands, suggesting that this measure indicates a capacity for executing demanding manual tasks.

Anodal transcranial direct current stimulation over premotor cortex facilitates observational learning of a motor sequence.

Motor skills, including complex movement sequences, can be acquired by observing a model without physical practice of the skill, a phenomenon known as observational learning. Observational learning of motor skills engages the same memory substrate as physical practice, and is thought to be mediated by the action observation network, a bilateral fronto‐parietal circuit with mirror‐like properties. We examined the effects of anodal transcranial direct current stimulation (tDCS) over premotor cortex, a key node of the action observation network, on observational learning of a serial response time task. Results showed that anodal tDCS during observation of the to‐be‐learned sequence facilitated reaction times in the subsequent behavioral test. The study provides evidence that increasing excitability of the action observation network during observation can facilitate later motor skill acquisition.