Changes in Gray Matter Induced by Learning—Revisited

BACKGROUND: Recently, activation-dependant structural brain plasticity in humans has been demonstrated in adults after three months of training a visio-motor skill. Learning three-ball cascade juggling was associated with a transient and highly selective increase in brain gray matter in the occipito-temporal cortex comprising the motion sensitive area hMT/V5 bilaterally. However, the exact time-scale of usage-dependant structural changes occur is still unknown. A better understanding of the temporal parameters may help to elucidate to what extent this type of cortical plasticity contributes to fast adapting cortical processes that may be relevant to learning. PRINCIPAL FINDINGS: Using a 3 Tesla scanner and monitoring whole brain structure we repeated and extended our original study in 20 healthy adult volunteers, focussing on the temporal aspects of the structural changes and investigated whether these changes are performance or exercise dependant. The data confirmed our earlier observation using a mean effects analysis and in addition showed that learning to juggle can alter gray matter in the occipito-temporal cortex as early as after 7 days of training. Neither performance nor exercise alone could explain these changes. CONCLUSION: We suggest that the qualitative change (i.e. learning of a new task) is more critical for the brain to change its structure than continued training of an already-learned task

Mean effects analysis.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002669#pone-0002669-g003" target="_blank">Figure 3</a> top: The mean effect analysis of the previous data set (1.5 Tesla) of 12 volunteers <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002669#pone.0002669-Draganski1" target="_blank">[1]</a> and the present data set (3 Tesla) of 20 volunteers showed that both cohorts exhibit transient gray matter increase in the hMT/V5 bilaterally (right: x = 41, y = −82, z = 4; Z = 4.06; left: x = −38, y = −80, z = 2; Z = 3.12). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002669#pone-0002669-g003" target="_blank">Figure 3</a> bottom: Box plot of the parameter estimates for both samples in the MT-area (right hMT/V5) using the contrasts described in the text to test for medium effects in both groups (no conjunction). The cluster is displayed with p<0.001 (uncorr.) and all parameter estimates (betas) in this cluster were averaged.</p

Transient structural changes superimposed on a normalized T1-image.

<p>Gray matter increase is shown superimposed on a normalized T1-image. The left side of the picture is the left side of the brain. a.u. = arbitrary units. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002669#pone-0002669-g001" target="_blank">Figure 1</a> top: Statistical parametric maps demonstrating the transient structural changes during the time of skilled performance (scans 2–4) compared to time point 1. A significant gray matter increase was found in the midtemporal area (hMT/V5) and in the frontal and temporal lobes and the cingulate cortex bilaterally. This pattern reversed when study participants were examined at time points 5 and 6 (following the weeks of exercise). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002669#pone-0002669-g001" target="_blank">Figure 1</a> bottom: mean and 90% confidence interval of the voxels of maximum intensity (right hMT) representing the gray matter expansion over time. Each box represents one scan (scan 1 =  before training, scans 2–4 = 7, 14 and 21 days after scan one and during the exercise period; scan 5 after two and scan 6 after four months (after training had stopped.)</p

Higher phage virulence accelerates the evolution of host resistance

Pathogens vary strikingly in their virulence and the selection they impose on their hosts. While the evolution of different virulence levels is well studied, the evolution of host resistance in response to different virulence levels is less understood and, at present, mainly based on observations and theoretical predictions with few experimental tests. Increased virulence can increase selection for host resistance evolution if the benefits of avoiding infection outweigh resistance costs. To test this, we experimentally evolved the bacterium Vibrio alginolyticus in the presence of two variants of a filamentous phage that differ in their virulence. The bacterial host exhibited two alternative defence strategies: (1) super infection exclusion (SIE), whereby phage-infected cells were immune to subsequent infection at the cost of reduced growth, and (2) surface receptor mutations (SRM), providing resistance to infection by preventing phage attachment. While SIE emerged rapidly against both phages, SRM evolved faster against the high- than the low-virulence phage. Using a mathematical model of our system, we show that increasing virulence strengthens selection for SRM owing to the higher costs of infection suffered by SIE immune hosts. Thus, by accelerating the evolution of host resistance, more virulent phages caused shorter epidemics.ISSN:0080-4649ISSN:0950-1193ISSN:1471-2954ISSN:0962-845