required for both types of perception [7,13–15]. As there is only a relatively small body of literature investigating age-related changes in haptics [16,17], we aimed to investigate the influence of reduced tactile acuity and cognitive capacity on the haptic performance of older adults. Age-related factors contributing to the loss of tactile acuity and cognition Physiological brain aging is characterized by a number of alterations that provoke age-dependent decline of sensory processing, motor performance, and cognitive function [18–20]. Age-related changes develop at all stages of the somatosensory processing pathway. Skin conformance is altered [21,22] and the density of Meissner’s and Pacinian corpuscles decreases in old age [23–25], while Merkel-neurite complexes might possibly be less affected [23,25]. Additionally, nerve conduction velocity and sensory nerve action potentials slow down [26–28]. These changes are thought to be due to an age-related reduction in the number and density of myelinated peripheral nerve fibers, as well as a decrease in thickness of the myelin in the remaining fibers [29,30]. Furthermore, there is evidence of substantial decline in gray matter density of the aged human brain [31,32]. Along with neuronal apoptosis and the loss of synaptic contacts described in some regions of the brain [33–35], as the brain ages, the concentrations of acetylcholine, noradrenaline, dopamine, and GABA and NMDA receptors [36] decrease. These changes, along with altered functional activation patterns [37], dramatically affect somatosensory information processing as has been repeatedly demonstrated for tactile discrimination performance [37–45]. Experiments in adults revealed that adding constraints to the manual exploration process, i.e. reducing cutaneous information (spatial, temporal and thermal) or kinesthetic information (spatial and temporal) significantly impairs haptic perception [46]. These experiments resemble to some extent conditions arising during the human aging process thereby highlighting the dramatic impact of age on haptic performance. Cognitive aging manifests as a mild age-related decline in cognitive functions with highly individual changes in general cognitive capacity, as well as domain-specific declines in fluid reasoning, mental processing speed, episodic memory, and spatial ability [47–49]. The mechanisms that are thought to underlie these decreases fall into 2 general categories [19]. On the one hand, one global undifferentiated mechanism, such as cognitive processing-speed, could account for the loss of performance [50]. On the other hand, the age-related decline might be caused by specific cognitive mechanisms, such as executive functioning, which is used in service of many cognitive tasks, occurring in everyday life or work related tasks [51]. Interdependence between sensorimotor functioning and cognition in later life The majority of investigations into age-related decline of sensory, sensorimotor, and cognitive functions have looked at the components individually, but it is generally accepted that the loss of functional integrity between the domains is functionally coupled [52,53]. In recent years, a number of studies have reported an increase in co-variation or interdependence between sensory and cognitive functions in old age [54,55,52,56,57]. Data from large-scale cross-sectional and longitudinal studies such as the Berlin aging study (BASE, [58]) showed strong relationships between intellectual and sensory functioning in old age [56]. Experimental studies investigating the relationship between sensory functions and cognition used either a simulated loss of Haptic Performance in Later Life sensation to explore the effects on cognitive function [59–61], or cognitive load manipulations on sensorimotor performance [62,63]. In general, both interventions affected older adults’ performance more than that of younger adults. Some authors hypothesized that sensory and sensorimotor declines may precede and predict cognitive decline [64,65], whereas others refrained from assigning priority to any of the 3 domains, but favored either a common cause affecting all functions [52], an increase in cross- domain resource competition, or a combination of both [66]. Particularly in old age, sensory, sensorimotor, and cognitive performance determines the extent to which a mobile and independent life is possible [53]. For this reason, the investigation of the development of these processes into late adulthood is not only of general interest, but offers a direct link to gerontological practice [18,19]. In the present study, we investigated the extent to which the age-related decline in haptic performance is related to the individual loss of tactile acuity and cognitive capacity. Results Haptic performance The haptic performance of all subjects declined with increasing age (Pearson correlation, N = 78, r = 0.479, p#0.001), with the decline being stronger in female subjects (Pearson correlation, N = 47, r = 0.585, p#0.001) as compared to male subjects (Pearson correlation, N = 31, r = 0.417, p = 0.010) (fig. 1A). We found a significant interaction of the subjects’ age and gender with their haptic performance (AGE*GENDER: F(1,31) = 17.535; p#0.001) indicating a stronger age-related increase of the number of errors in the cross-modal haptic task for female subjects (fig. 1B). Tactile performance Tactile performance, as assessed by the two-point discrimina- tion test, declined with increasing age (Pearson correlation, N = 79, r = 0.430, p#0.001) in both male (Pearson correlation, N = 31, r = 0.469, p = 0.004) and female subjects (Pearson correlation, N = 48, r = 0.408, p = 0.002) (fig. 2A). For tactile performance, we found no interaction of the subjects’ age and gender (AGE*GEN- DER: F(1,32) = 2.942; p = 0.096) indicating almost the same degree of age-related decline in tactile performance for both male and female subjects (fig. 2B). Cognitive performance The subjects’ cognitive performance was rated based on the results of the Raven Standard Progressive Matrices (RSPM) test. The percentage of correct answers declined with increasing age (Pearson correlation, N = 81, r = 20.550, p#0.001) for both male (Pearson correlation, N = 32, r = 20.580, p#0.001) and female subjects (Pearson correlation, N = 49, r = 20.582, p#0.001) (fig. 3A). The investigation of the subjects’ performance revealed a significant interaction for age and gender (AGE*GENDER: F(1,33) = 22.307; p#0.001) indicating a stronger age-related decline of cognitive performance in female subjects (fig. 3B) Correlation of haptic, tactile, and cognitive performance Second order partial correlations controlling for the age of subjects were used to investigate the relationships between tactile, haptic, and cognitive performance. Regarding all subjects’ tactile and haptic performance we found no significant correlation (partial correlation corrected for AGE, N = 74, r = 0.133, p = 0.126). In contrast, this correlation was found to be significant in the male subpopulation (partial correlation corrected for AGE, N = 28, r = 0.342, p = 0.032) but not of female subjects (partial PLoS ONE | www.plosone.org 2 January 2012 | Volume 7 | Issue 1 | e30420