The primary aim of this study was to determine the extent to which human MT+/ V5, an extrastriate visual area known to mediate motion processing, is involved in visuomotor coordination. To pursue this, the excitability of MT+/ V5, primary motor, and primary visual cortex was increased or decreased by the application of seven minutes of anodal and cathodal transcranial direct current stimulation (tDCS) in healthy human subjects while they were performing a visuomotor tracking task involving hand movements.
The percentage of correct tracking movements increased specifically during and immediately after cathodal stimulation, which decreases cortical excitability, only when V5 was stimulated. None of the other stimulation conditions affected visuomotor performance. The researchers propose that the improvement in performance caused by cathodal tDCS of V5 is due to a focusing effect on the complex motion perception conditions involved in this task.
This hypothesis was proven by additional experiments: When testing simple and complex motion perception in dot kinetograms, it was found that a diminution in excitability induced by cathodal stimulation improved the subject’s perception of the direction of the coherent motion only if this was presented among random dots (complex motion perception), and worsened it if only one motion direction was presented (simple movement perception). The data suggest that area V5 is critically involved in complex motion perception and identification processes important for visuomotor coordination.
The results also raise the possibility of the usefulness of tDCS in rehabilitation strategies for neurological patients with visuomotor disorders. Article 2 Environmental stimulation, parental nurturance and cognitive development in humans Martha J. Farah, Laura Betancourt, David M. Shera, Jessica H. Savage, Joan M. Giannetta, Nancy L. Brodsky, Elsa K. Malmud and Hallam Hurt 1. Department of Psychology and Center for Cognitive Neuroscience, University of Pennsylvania, USA 2. Division of Biostatistics and Epidemiology, Department of Pediatrics,
Children’s Hospital of Philadelphia and University of Pennsylvania; Department of Epidemiology and Biostatistics, University of Pennsylvania, USA 3. Division of Neonatology, Department of Pediatrics, University of Pennsylvania and Children’s Hospital of Philadelphia, USA Developmental Science 11:5 (2008), pp 793-801 The effects of environmental stimulation and parental nurturance on brain development have been studied extensively in animals. Much less is known about the relations between childhood experience and cognitive development in humans.
Using a longitudinally collected data set with ecologically valid in-home measures of childhood experience and later in-laboratory behavioral measures of cognitive ability, the researchers were able to test hypotheses concerning the effects of environmental stimulation and parental nurturance. A double dissociation was found: On one hand, there was a selective relation between parental nurturance and memory development, consistent with the animal literature on maternal buffering of stress hormone effects on hippocampus development.
On the other hand, there was a selective relation between environmental stimulation and language development. The results primarily suggest that the same general dimensions of early life experience identified as important in animal studies of brain development are also important for humans. In particular, the relation between the composites measuring parental nurturance and later memory ability, which have no common-sense connection, is consistent with studies of experience and brain development in animals. The present findings thus provide an important bridge between the study of neurocognitive development in animals and humans.
Secondarily, variation in the childhood experience of healthy humans bears a systematic relationship to cognitive development, and this relationship is more selective and specific than simply better environments predicting better development. Memory development is predicted by parental nurturance but not environmental stimulation, whereas language development is predicted by environmental stimulation, but not parental nurturance. Finally, these effects represent a possible mechanism by which socioeconomic status is associated with intellectual attainment. Article 3 MEG Study of Short-Term Plasticity Following Multiple
Digit Frequency Discrimination Training in Humans Lichan Liu and Andreas A. Ioannides Laboratory for Human Brain Dynamics, RIKEN Brain Science Institute (BSI), 2-1 Hirosawa, Wakoshi, Saitama, Japan. Brain Topography, Volume 16, Number 4, Summer 2004 The researchers trained four right-handed male subjects to detect small changes in the frequency of 21 Hz electrical stimulation applied to digits 2+3+4 of the right hand for four hours. Before and after the training, magnetoencephalographic (MEG) signals were recorded when the stimulation was applied to digit 2-5 separately using a whole-head MEG system.
Tomographic analysis was applied to the MEG data to track the evolution of activity over the entire brain every 1. 6 ms and evaluated the change for each digit before and after the training. In summary: (1) subjects improved in discrimination performance with training; (2) activations were identified in the left primary somatosensory (L-SI) and medial parietal precuneus (PCu) areas, but no systematic changes were observed in location and strength of activation of these two areas; (3) after training in L-SI, the 21Hzspectral power increased
for digits 3 and 4 over the stimulation period, while the 10 Hz spectral power increased for digit 3 around stimulus onset and offset; (4) only digit 3 showed significant change of correlation between L-SI and PCu areas around the stimulus onset and offset, coincident with the increased 10 Hz spectral power. The results suggest that short-term plasticity is associated with changes in timing and interaction between cortical areas. Discussion
The main finding of the first study is that cathodal tDCS applied to the left V5 improved performance in a visuomotor coordination task that encompassed both dynamic, high-resolution perception and selection of motion predetermined by a moving target. Stimulation of the primary visual cortex and the left motor cortex did not result in significant changes in performance, nor were the reaction times in the random dot kinetogram task significantly affected. These results suggest that tDCS indeed modified visual motion perception and motor performance.
Common sense says that childhood experience affects cognitive development. Yet common sense does not say which psychological or brain functions will be affected by experience, or which specific aspects of childhood experience will exert an effect. The second study attempts to address these issues empirically with a unique longitudinally collected data set including ecologically valid in-home measures of early childhood experience and later laboratory measures of cognitive function. The effects found were strikingly selective and, in addition to their statistical significance, were substantial in size.
In the third study, functional rather than anatomical short-term plastic changes in the brain induced by the frequency discrimination task were identified. After training, no new activated areas or expansion of activated areas or systematic increases in activation strength in any one specific area were observed. Instead, increased spectral power around 21 Hz in L-SI for both trained digits 3 and 4 for all 4 subjects was observed. Furthermore, for digit 3, increased spectrum power at 10 Hz in L-SI for all 4 subjects between map I and II around the
stimulus onset and offset was observed. Conclusion After analyzing the above three methods of brain stimulation, one can come to the conclusion that the first study was found to have the maximum results in term of invoking activity of the stimulated areas. The study stands out among the other two not just for its methodology, but also for its high reliability and accuracy. Hence, transcranial direct current stimulation (tDCS) can be considered to be the best method of brain stimulation.