Underlying Mechanisms
Lawton, T. and Huang, M.X. (2019) Dynamic Cognitive Remediation for a Traumatic Brain Injury (TBI) Significantly Improves Attention, Working Memory, Processing Speed, and Reading Fluency, Restorative Neurology and Neuroscience, 37, 71–86. DOI 10.3233/RNN-180856
Click here to download
[As described in Lawton and Stephey (2009)] Click here to download
One possible neurobiological mechanism for the timing deficits experienced by older adults is that sluggish magnocellular (motion) neurons found in the dorsal or ‘where’ pathway, including the Lateral Geniculate Nucleus (LGN) and cortical areas V1 (striate cortex) and the Medial Temporal (MT) cortex, make it difficult to attend in direction discrimination tasks, since magnocellular neurons would not signal in advance of the linked pattern or parvocellular neurons. It is likely that the ability of magnocellular neurons to bracket the activity of linked parvocellular neurons over time is what has been disrupted, resulting in temporal and spatial sequencing deficits that cause navigation to be more difficult and causes a reduction in the field of view. Since physiological data demonstrate that magnocellular neurons control the gain of the direction-discrimination network, it is plausible that the older adultís more sluggish, immature magnocellular neurons might be causing a deficit in attentional focus, preventing the linked parvocellular neurons from isolating and sequentially processing the relevant information needed when navigating, especially at night (low light levels) and under stress (more effort needed to complete the task).
Previous results suggest that pictorial working memory, as needed for navigation, is coded by the temporary activation of an ensemble of neurons in the region of the association cortex that processes visual information, rather than by neuronal activity in a brain area specialized for short-term memory tasks. Visual working memory is needed for navigation and driving, a task that some find much more difficult as they age. Neurons with memory-related responses have been reported in multiple brain regions, for example, the posterior parietal and inferior temporal cortices, which are the end stages of the dorsal and ventral visual pathways, respectively. The dorsal prefrontal cortex is connected with the posterior parietal cortex, whereas the ventral prefrontal cortex is linked to the inferior temporal cortex. On the basis of this organization, Goldman-Rakic proposed that working memory is mediated by the sustained activity of neurons in parallel, distributed cortical networks. FMRI studies have verified the concurrent activation of multiple human brain areas during performance of cognitive tasks that engage working memory, confirming the findings of the monkey neurophysiological studies.
Recent fMRI and PET studies indicate that older adults have more prefrontal activation as a result of expending more effort to complete tasks, when compared to younger adults. Studies describe the increased activity in prefrontal cortex as due to recruiting additional prefrontal regions to prevent the performance of older adults from declining. This is supported by finding that prefrontal cortical activity was reduced similarly by aging and by a divided attention task, suggesting that increasing age and effortful cognitive processing put an equal claim on the available attention resources. Practice requiring less conscious processing has been associated with a decrease in frontal activity. Moreover, left-lateralized (ventral) prefrontal activity (encoding information) that is more active than right-lateralized (dorsal) prefrontal activity (retrieving information) in young adults, is equal in older adults, suggesting more effort must be made by older adults to retrieve information from working memory for higher cognitive processing like navigation.
The increased activity in the dorsal pathways of older adults required to retrieve information is consistent with the timing of magnocellular pathways having degraded over time. Moreover, Lawton and Stephey (2009) showed that training on direction discrimination, designed to strengthen magnocellular activity, increased the ability of the dorsal pathway to improve both navigation and memory, in addition to attentive and sequential processing.
These studies provide evidence that that in older adults the timing in their brain is disrupted, affecting attention, processing speed, memory, and navigation. Processing speed and attention have been found to explain a large part of age-related memory deterioration. Reduced information processing speed may explain problems in memory encoding and retrieval because this mental slowing can lead to superficial processing and inefficient strategies where elaboration is required.
TBI patients with severe injuries who have used PATH therapy have improved up to 10 fold in cognitive processing skills, including multi-tasking, focusing attention, memory, and sequential processing after a severe TBI. This improvement is dramatic and permanent!
Lawton, T. and Huang, M.X. (2019) Dynamic Cognitive Remediation for a Traumatic Brain Injury (TBI) Significantly Improves Attention, Working Memory, Processing Speed, and Reading Fluency, Restorative Neurology and Neuroscience, 37, 71–86. DOI 10.3233/RNN-180856
Click here to download
Lawton, T. and Stephey, D. (2009) “Training direction discrimination improves usable field of view, short term memory, and navigation in older adults”, Optometry and Vision Development, 40:2, 82-93.
Click here to download
