Infection impairs problem-solving performance in American crows

Infectious disease and cognition in wild populations

“…Evidence for infection-linked impairment of cognitive performance is widespread, albeit variable, across host and parasite taxa and across cognitive abilities, including learning, memory, and problem-solving. Impaired performance on associative learning tasks, for example, follows infection with the trypanosome Crithidia bombi in bumblebees (Bombus impatiens) [24], and lower problem-solving performance has been documented in American crows (Corvus brachyrhynchos) naturally infected with the bacterial pathogen Campylobacter jejuni [16] and female (but not male) great tits (Parus major) infected with the blood protozoan Plasmodium [14]. Likewise, impaired performance on spatial memory tasks has been observed among laboratory rodents infected with bacteria and nematodes [12,13].…”

“…Challenges in studies of infection-linked cognitive impairment One challenge in all studies of cognitive ecology is the scarcity of comparable data across taxa [22,23,78]. The number of studies that test links between cognition and infection is limited, as is the taxonomic breadth of hosts: most research has focused on humans [11,53], laboratory rodents [12,13], bees [17,24], and birds [14][15][16]. Moreover, because of differences in behavior, sensory modalities, and physical abilities, cross-species comparisons of cognitive performance must draw inferences from different, taxon-specific cognitive tests.…”

“…In contrast, the infection-cognition link in rodents has often focused on impairments of spatial memory using the Morris water maze [12,13], in which swimming animals must remember the location of a submerged, hidden platform (Figure IB). In birds, this link has been evaluated through performance on a variety of problem-solving tests [14,16], such as a string-pulling task requiring the bird to pull and step on a string to retrieve a food reward (Figure IC). A pattern of parasite-linked cognitive impairment has emerged despite the diversity of experimental paradigms used.…”

“…Variation in common testing paradigms of cognition. Testing paradigms vary among studies from (A) the proboscis extension reflex to test learning in bees [17], (B) the Morris water maze test of spatial memory in rodents [12,13], and (C) string-pulling tests to assess problem-solving in birds [16].…”

“…Although difficult to disentangle from neuroimmune activation (discussed next; [55,56]), sickness behaviors could impair cognitive performance in part because sick animals are less motivated to explore their environment or perform cognitively challenging tasks, particularly those with a food reward. In wild-caught American crows, for example, individuals with natural C. jejuni infections were less likely to solve a string-pulling task with a food reward than uninfected birds (see Figure IC in Box 2), in part, because infected birds were less likely to attempt the task [16]. Likewise, in rodent studies, the impacts of LPS and IL-1 on performance in a spatial memory task (Morris water maze; see Figure IB in Box 2) can be short-lived, reversible, or contextdependent, indicating that some manifestations of cognitive impairment could reflect changes in motivation or emotional state, rather than a change in cognitive ability [55].…”