Size and Reversal Learning in the Beagle Dog as a Measure of Executive Function and Inhibitory Control in Aging

Abstract

Several studies converge on the idea that executive processes age earlier than other cognitive processes. As part of a larger effort to investigate age-related changes in executive processes in the dog, inhibitory control was measured in young, middle-aged, old, and senior dogs using size discrimination learning and reversal procedures. Compared to young and middle-aged dogs, old and senior dogs were impaired on both the initial learning of the size task and the reversal of original reward contingencies. Impaired performance in the two aged groups was characterized as a delay in learning the correct stimulus-reward contingencies and, among the senior dogs in particular, an increase in perseverative responding. These separate patterns of reversal impairments in the old and senior dogs may reflect different rates of aging in subregions of the frontal cortex.Inhibitory control and performance monitoring are critical executive functions of the human brain which show decreased efficiency during normal aging (McDowd and Oseas

Assessment of nutritional interventions for modification of age-associated cognitive decline using a canine model of human aging

“…As mentioned previously, Ab typically is deposited early in the prefrontal cortex of both dogs (Head et al 2000) and humans (Braak and Braak 1997). Cognitive tasks thought to be dependent on the prefrontal cortex are impaired by age more consistently and earlier in the dog (Tapp et al 2003a(Tapp et al , b, 2004a. Further, the frontal lobes selectively atrophy in aged dogs prior to overall brain atrophy (Tapp et al 2004a).…”

“…Procedural learning and memory, as well as simple discrimination learning, are generally insensitive to aging (Milgram et al 1994). By contrast, tests of executive function, such as discrimination reversal learning (Milgram et al 1994;Tapp et al 2003a), and working memory (Adams et al 2000b;Head et al 1995), such as a delayednonmatching-to-position (DNMP) task (Chan et al 2002), are highly sensitive to aging. In other instances, age sensitivity depends on prior test experience.…”

“…Using a cross-sectional approach, we have established that tasks dependent on frontal lobe function, in particular tests of executive function (Milgram et al 1994;Tapp et al 2003a) and visuospatial working memory (Chan et al 2002), are notably sensitive to age (Adams et al 2000b;Head et al 1995). In a study of 109 dogs (manuscript in preparation), a statistically significant impairment in both acquisition of the DNMP using a 5-s delay and memory capacity were detected as early as six years of age (Figure 1) (Araujo 2004;Araujo et al 2004a).…”

Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: Relevance to Alzheimer's disease

“…The cognitive enrichment consisted of a landmark discrimination task, an oddity discrimination task [78], and size concept learning [109]. In addition, all animals, regardless of treatment condition were evaluated annually on a test of visuospatial memory [36], object recognition memory [30] and either size discrimination and reversal learning [108], or black/white discrimination and reversal on consecutive years.…”

“…Aged canines show reduced cerebral volume, cortical atrophy and ventricular widening by in vivo magnetic resonance imaging [103,110,111]. The aging canine also shows impairments in visuospatial working memory and executive function [36,102,108]. Aged beagle brain accumulates amyloid-β-peptide (Aβ) that is of the same sequence as humans [63,96] and is correlated with decline in cognitive function with age [43,51].…”