Psychology Ph.D. Dissertations

Title

Neurocognitive aging in homing pigeons (Columba livia): Further investigation into hippocampal-dependent memory impairment and testing of the cholinergic hypothesis of cognitive decline

Date of Award

2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Psychology

First Advisor

Verner Bingman (Advisor)

Second Advisor

Brooks Vostal (Other)

Third Advisor

Richard Anderson (Committee Member)

Fourth Advisor

Jari Willing (Committee Member)

Abstract

Despite decades of neurocognitive aging research in mammals, it was not until recently that studies of neurocognitive aging in birds surfaced. Indeed, it was not until 2014 that the first reports of age-related, spatial-cognitive deficits in homing pigeons were published. It was first hypothesized that the observed cognitive deficits resulted, in part, from hippocampal formation (HF) degeneration similar to that seen in mammals. However, multiple reports have since found the HF of older, memory-impaired pigeons to be larger and contain more neurons than the HF of younger, non-impaired pigeons. As an alternative explanation for the declining spatial-cognitive ability of birds, it was hypothesized in the current dissertation that activation of the old HF would be reduced during learning of a spatial-cognitive task. To test this hypothesis, HF activation (measured via expression of the activity-dependent immediate early gene, c-Fos) in response to a spatial working memory challenge was compared between younger and older pigeons. Additionally, the effects of age on activation of the septum and nucleus of the diagonal band (NDB), which are believed to influence HF functioning, and on the number of cholinergic neurons in these regions was examined. Highlighting the important findings include: compared to younger pigeons, older pigeons had (i) decreased HF and septum neuronal activation during spatial learning, (ii) fewer cholinergic (i.e., ChAT-expressing) neurons in the septum, (iii) a stronger correlation between the number of cholinergic septal neurons and HF neuronal activity, and (iv) weaker correlated neuronal activity between NDB and HF. In summary, the data support the hypothesis that activation of the old HF would be reduced during learning of a spatial-cognitive task, as well as identifies neural correlates (functional/activational and neurochemical) of age-related, spatial-cognitive decline in pigeons in other, HF-connected regions.

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