Chapter 24

Pushing harder on that accelerator, in reverse!
How ‘negative learning’ can speed up age- and brain injury-related decline

  1. Age related differences in gait patterns have been recorded in many studies. You can begin with Seung-uk K et al (2010) Age-associated differences in the gat pattern changes of older adults during fast-speed and fatigue conditions: results from the Baltimore longitudinal study of ageing. Age Ageing 39:688; or in a study more directly related to falling dynamics, McIlroy WE & Maki BE (1996) Age-related changes in compensatory stepping in response to unpredictable perturbations. J Gerontol A Biol Sci Med Sci 51:289. Slower stereotypic walking advances to more and more loss of control and less predictable ‘corrective’ actions under any challenging conditions. Because of changes in gait and postural stability, you engage muscles across the ankle and knee to sustain balance via their co-contraction, which adds to your dangers. See, for example, Benjuva N et al (2004) Aging-induced shifts from a reliance on sensory input to muscle cocontraction during balanced standing. J Gerontol A Biol Sci Med Sci 59:166. In the end, when your posture is perturb, you just can’t respond in time to save your bacon. See, for example, van den Bogert AJ et al (2002) Response time is more important than walking speed for the ability of older adults to avoid a fall after a trip. J Biomechan 35:199. Your slow responses extend, of course, to any corrective action that might save you from the fall. See, for example Cheng KC et al (2012) Does aging impair the capacity to use stored visuospatial information or online visual control to guide reach to grasp reactions evoked by unpredictable balance perturbation? J Gerontol A Biol Sci Med Sci 67:1338.
  2. We have conducted extensive studies demonstrating sound intensity-specific plasticity. They show that when we expose a brain as a listener to sounds at a specific level, it ‘specializes’ for sound reception in a narrow intensive range, and degrades listening for louder or softer sounds. When you turn the volume up on the television or radio, your brain will rapidly adapt in ways that favor that volume range. See Polley DB et al (2004) Associative learning shapes the neural code for stimulus magnitude in primary auditory cortex. PNAS 101:16351; and Polley DB et al (2006) Perceptual learning directs auditory cortical map reorganization through top-down influences. J Neurosci 26:4970.
  3. The decline in the “useful field of view” (UFOV) with age was initially described as a contraction of the field that an individual commands in visual space. See Ball K, Owsley C (1993) The useful field of view test: a new technique for evaluating age-related declines in visual function. J am Optom Assoc 64:71. More recently, studies have argued that deficits arise from attentional inefficiency that disfavors more-peripheral viewing, and that degrades broader scene reconstruction. See, for example, Sekuler AB et al (2000) Effects of aging on the useful field of view. EXP aging Res 26:103; or Cosman JD et al (2012) Visual search for features and conjuctions following declines in the useful field of view. Exp Aging Res 38:411. The fact that UFOV training positively impacts attention circuits in the brain of elder subjects (is consistent with this interpretation.
  4. For an entre into studies of eye movements in aging, begin with Peltsch A et al (2011) Age-related trends in saccade characteristics among the elderly. Neurobiol Aging 32:669; and for that age-related decline of responses to novel stimuli, see Insel N et al (2008) Aging in rhesus macaques is associated with changes in novelty preference and altered saccade dynamics. Behav Neurosci 122:1328; or for an exemplar from a series of studies documenting neurological weakening of responses to novel stimuli, see Knight RT (1987) Aging decreases auditory event-related potentials for unexpected stimuli in humans. Neurobiol Aging 8:109. Interestingly, in contrast with the young’uns, older individuals differentially spend more time holding their eyes on positive vs negative images. See, for example, Isaacowitz DM et al (2006) Selective preference in visual fixation away from negative images in old age? An eye-tracking study. Psychol Aging 21:40.
  5. The relationship between saccade rates and visual recognition has been an especially interesting recent study of investigation in animal models. For an entre into this literature, begin with DiCarlo JJ et al (2012) How does the brain solve visual object recognition? Neuron 73:415.
  6. The impacts of visual decline on motor vehicle accident rates, and on the kinds of motor accidents that predominate for individuals of an older age, are documented in the notes related to Chapter xx.
  7. Thousands of studies in experimental psychology and neuroscience document the role of ‘motivation’ for empowering learning. They require no further, special annotation here!
  8. There is a long history of animal studies demonstrating the fundamental role of the hippocampus in navigation. In humans, one of the most cited brain imaging studies in history documents the positive impacts, for the size of your hippocampus, of completing the 3-year navigation training program to obtain your license as a London taxi driver. See Maguire EA (2000) Navigation-related structural change in the hippocampi of taxi driers. PNAS 94:4398. Veronique Bohbot and colleagues (McGill University) made an interesting comparison of hippocampus activity in elder subjects who routinely did vs did not use GPS while driving. See This WAS a case of use it, and lose it.