Deborah M. Saucier

Enriched childhood experiences moderate age-related motor and cognitive decline

Aging is associated with deterioration of skilled manual movement. Specifically, aging corresponds with increased reaction time, greater movement duration, segmentation of movement, increased movement variability, and reduced ability to adapt to external forces and inhibit previously learned sequences. Moreover, it is thought that decreased lateralization of neural function in older adults may point to increased neural recruitment as a compensatory response to deterioration of key frontal and intra-hemispheric networks, particularly of callosal structures. However, factors that mediate age-related motor decline are not well understood. Here we show that music training in childhood is associated with reduced age-related decline of bimanual and unimanual motor skills in a MIDI keyboard motor learning task. Compared to older adults without music training, older adults with more than a year of music training demonstrated proficient bimanual and unimanual movement, evidenced by enhanced speed and decreased movement errors. Further, this group demonstrated significantly better implicit learning in the weather prediction task, a non-motor task. The performance of older adults with music training in those tasks was comparable to young adults. Older adults, however, displayed greater verbal ability compared to young adults irrespective of a past history of music training. Our results indicate that music training early in life may reduce age-associated decline of neural motor and cognitive networks.

Sex differences in object location memory and spatial navigation in Long-Evans rats

In both humans and rodents, males typically excel on a number of tasks requiring spatial ability. However, human females exhibit advantages in memory for the spatial location of objects. This study investigated whether rats would exhibit similar sex differences on a task of object location memory (OLM) and on the watermaze (WM). We predicted that females should outperform males on the OLM task and that males should outperform females on the WM. To control for possible effects of housing environment, rats were housed in either complex environments or in standard shoebox housing. Eighty Long-Evans rats (40 males and 40 females) were housed in either complex (Complex rats) or standard shoebox housing (Control rats). Results indicated that males had superior performance on the WM, whereas females outperformed males on the OLM task, regardless of housing environment. As these sex differences cannot be easily attributed to differences in cognitive style related to linguistic processing of environmental features or to selection pressures related to the hunting gathering evolutionary prehistory of humans, these data suggest that sex differences in spatial ability may be related to traits selected for by polygynous mating strategies.

Seasonal and sex differences in the hippocampus of a wild rodent.

Studies across and within species suggest that hippocampus size is sexually dimorphic in polygamous species, but not in monogamous species. Although hippocampal volume varies with sex, season and mating system, few studies have simultaneously tested for sex and seasonal differences. Here, we test for sex and seasonal differences in the hippocampal volume of wild Richardsons ground squirrels (Urocitellus richardsonii), a polygamous species that lives in matrilineal, kin-based social groups and has profound sex differences in behavior. Based on the behavior and ecology of this species, we predicted that males would have a significantly larger hippocampus than females and that the hippocampus would be largest in males during the breeding season. Analyses of both absolute and relative volumes of the hippocampus yielded a significant difference between the sexes and seasons as well as an interaction between the two such that non-breeding males have significantly larger hippocampal volumes than breeding males or females from either season. Dentate gyrus, CA1 and CA3 subfield volumes were generally larger in the non-breeding season and in males, but no significant interaction effects were detected. This sex and seasonal variation in hippocampal volume is likely the result of their social organization and male-only food caching behavior during the non-breeding season. The demonstration of a sex and seasonal variation in hippocampal volume suggests that Richardsons ground squirrel may be a useful model for understanding hippocampal plasticity within a natural context.

Sex Difference in Cue Strategy in a Modified Version of the Morris Water Task: Correlations between Brain and Behaviour

Background Sex differences in spatial memory function have been reported with mixed results in the literature, with some studies showing male advantages and others showing no differences. When considering estrus cycle in females, results are mixed at to whether high or low circulating estradiol results in an advantage in spatial navigation tasks. Research involving humans and rodents has demonstrated males preferentially employ Euclidean strategies and utilize geometric cues in order to spatially navigate, whereas females employ landmark strategies and cues in order to spatially navigate. Methodology/Principal Findings This study used the water-based snowcone maze in order to assess male and female preference for landmark or geometric cues, with specific emphasis placed on the effects of estrus cycle phase for female rat. Performance and preference for the geometric cue was examined in relation to total hippocampal and hippocampal subregions (CA1&2, CA3 and dentate gyrus) volumes and entorhinal cortex thickness in order to determine the relation between strategy and spatial performance and brain area size. The study revealed that males outperformed females overall during training trials, relied on the geometric cue when the platform was moved and showed significant correlations between entorhinal cortex thickness and spatial memory performance. No gross differences in behavioural performance was observed within females when accounting for cyclicity, and only total hippocampal volume was correlated with performance during the learning trials. Conclusions/Significance This study demonstrates the sex-specific use of cues and brain areas in a spatial learning task.

Housing environment and sex affect behavioral recovery from ischemic brain damage

In previous work from our laboratory, we have developed a model of stroke that allows the comparison of stroke injury across age groups (10-day old, 63-day old, 180-day old rats). In this current study, we incorporated environmental enrichment to determine whether this form of rehabilitation alters behavioral recovery, and whether age and/or sex interacts with enrichment. Our results indicated that ischemic male rats that were housed in standard cages (shoebox housed) performed the poorest on two tasks of motor ability, and that this performance was related to the size of the lesion. With the exception of lesion size, in which 10-day old enriched rats had significantly smaller lesions than either the enriched 63-day old rats or the 180-day old rats, we observed no significant effects of age on behavioral recovery. Thus, our results are consistent with the observation that male rats may be more vulnerable to stroke and that they may differentially benefit from enrichment.

Enriched environment and the effect of age on ischemic brain damage.

Stroke affects all age groups from the newborn to the elderly. Previous work from our laboratory has shown that despite a greater susceptibility to brain damage, the immature brain recovers more rapidly and to a greater extent than does the more mature nervous system. In the current study, we examined the influence of environmental enrichment on the effects of age on the brain damaging effects of stroke. Rats aged 10, 63, and 180 days received ischemic insults following stereotactic intra-cerebral injection of endothelin-1, and resulting in injury to the right middle cerebral artery territory. Rats were then housed in either environmentally enriched cages, or standard cages for 60 days, after which they were sacrificed, and brain volumes determined for the extent of neurologic injury. Rats receiving the insult at 10 days of age showed a reduction of pathologic injury when housed in the enriched cages compared to standard. Conversely, rats receiving the insult at 180 days and housed environmentally enriched cages actually showed an increased volume of brain damage compared to controls. Our findings clearly indicate the dramatic influence of age on the extent of stroke and the influence of rehabilitative therapies. Behavioral correlation to morphologic alterations is required. Attempts at therapeutic interventions clearly need to be age-specific.

Hummingbirds have a greatly enlarged hippocampal formation

Both field and laboratory studies demonstrate that hummingbirds (Apodiformes, Trochilidae) have exceptional spatial memory. The complexity of spatial–temporal information that hummingbirds must retain and use daily is probably subserved by the hippocampal formation (HF), and therefore, hummingbirds should have a greatly expanded HF. Here, we compare the relative size of the HF in several hummingbird species with that of other birds. Our analyses reveal that the HF in hummingbirds is significantly larger, relative to telencephalic volume, than any bird examined to date. When expressed as a percentage of telencephalic volume, the hummingbird HF is two to five times larger than that of caching and non-caching songbirds, seabirds and woodpeckers. This HF expansion in hummingbirds probably underlies their ability to remember the location, distribution and nectar content of flowers, but more detailed analyses are required to determine the extent to which this arises from an expansion of HF or a decrease in size of other brain regions.

THE EFFECTS OF SEASON AND SEX ON DENTATE GYRUS SIZE AND NEUROGENESIS IN A WILD RODENT, RICHARDSON'S GROUND SQUIRREL (UROCITELLUS RICHARDSONII)

Sex and reproductive status affect hippocampal neurogenesis and dentate gyrus (DG) size in rodents. Relatively few studies, however, address these two effects simultaneously and even fewer studies address this issue in wild populations. Here, we examined seasonal and sex differences in neurogenesis and DG size in a wild, polygynous and social rodent, Richardsons ground squirrel (Uriocitellus richardsonii). Based on the behavioral ecology of this species, we predicted that both neurogenesis and DG size would be sexually dimorphic and the degree of dimorphism would be greatest in the breeding season. Using unbiased stereology and doublecortin (DCX) immunohistochemistry, we found that brain volume, DG size and number of DCX cells varied significantly between breeding and non-breeding seasons, but only brain volume and the number of DCX labeled cells differed between the sexes. Both sex and seasonal differences likely reflect circulating hormone levels, but the extent to which these differences relate to space use in this species is unclear. Based on the degree of seasonal differences in neurogenesis and the DG, we suggest that ground squirrels could be considered model species in which to examine hippocampal plasticity in an ecologically valid context.

Mental Rotational Ability Is Correlated with Spatial but Not Verbal Working Memory Performance and P300 Amplitude in Males

This study investigated how both sex and individual differences in a mental rotation test (MRT) influence performance on working memory (WM). To identify the neural substrate supporting these differences, brain electrical activity was measured using the event-related potential technique. No significant sex differences were observed in a test of verbal WM, however males were significantly faster than females to respond to probe stimuli in a test of spatial WM. This difference was no longer significant after controlling for differences in MRT score, suggesting that rotational ability mediates performance in the spatial memory task for both sexes. A posterior P300 was observed in both tasks as participants encoded information into memory, however the amplitude of the P300 correlated with RT in the spatial task but not in the verbal task. Individual differences in the MRT also correlated with RT and with the amplitude of the P300, but again only in the spatial task. After splitting the analysis by sex, partial correlations controlling for MRT revealed that for males, individual differences in rotational ability completely mediated the correlation between the P300 and RT in the spatial task. This mediating effect was not observed for the female participants. The results therefore suggest a relatively stronger association in males between innate mental rotational ability, spatial memory performance, and brain electrophysiological processes supporting spatial memory.

Online corrections can produce illusory bias during closed-loop pointing

This experiment examined whether the impact of pictorial illusions during the execution of goal-directed reaching movements is attributable to ocular motor signaling. We analyzed eye and hand movements directed toward both the vertex of the Müller–Lyer (ML) figure in a closed-loop procedure. Participants pointed to the right vertex of a visual stimulus in two conditions: a control condition wherein the figure (in-ML, neutral, out-ML) presented at response planning remained unchanged throughout the movement, and an experimental condition wherein a neutral figure presented at response planning was perturbed to an illusory figure (in-ML, out-ML) at movement onset. Consistent with previous work from our group (Heath et al. in Exp Brain Res 158:378–384, 2004; Heath et al. in J Mot Behav 37:179–185, 2005b), action-bias present in both conditions; thus illusory bias was introduced into during online control. Although primary saccades were influenced by illusory configurations (control conditions; see Binsted and Elliott in Hum Mov Sci 18:103–117, 1999a), illusory bias developed within the secondary “corrective” saccades during experimental trials (i.e., following a veridical primary saccade). These results support the position that a unitary spatial representation underlies both action and perception and this representation is common to both the manual and oculomotor systems.