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September 12, 2007

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What? Where? When? Some animals may know

Aug. 12, 2007
Special to World Science  

A long string of ex­pe­ri­ments over dec­ades have re­peat­edly found that an­i­mals aren’t as dumb as hu­mans tra­di­tion­ally thought they were. Far from it. But are they act­ually con­scious? 

The meadow vole Mi­cro­tus penn­syl­van­i­cus, a small ro­dent that tends to hide in tun­nels un­der the grass. It is one of the most com­mon small mam­mals in North Amer­i­ca. (Im­age cour­te­sy U.S. Nat'l Park Serv­ice)
Stud­ies have giv­en only vague glimpses of an an­swer. But some sci­en­tists have said an or­gan­ism must be con­scious if it has “ep­i­so­dic mem­o­ry.” This is ba­sic­ally the mem­o­ry of the “what, where and when” of events in life.

New re­search has found that some an­i­mals may have just this sort of mem­o­ry. 

Ro­dents known as mead­ow voles can “re­call the ‘what,’ ‘where,’ and ‘when’” of a past ev­ent, re­search­ers wrote in the ti­tle of a new study pub­lished in the re­search jour­nal An­i­mal Cog­ni­tion.

Al­though past stud­ies had sug­gested such abil­i­ties in an­i­mals, they in­volved put­ting the crea­tures through tests that in­volved some train­ing, the au­thors said. That opened the re­sults to crit­i­cism that the train­ing could have af­fect­ed their be­hav­ior in some way that made the an­i­mals merely act as though they knew “what, where and when.” The new study in­volved no pre-train­ing. 

It ex­ploited the fact that fe­male voles, along with some oth­er an­i­mals, en­ter a pe­ri­od of peak sex­u­al re­cep­ti­vity just af­ter giv­ing birth. The some­what sur­pris­ing ten­den­cy may be ex­plained by the crea­tures’ short life­span, which com­pels them to pack a lot of re­pro­duc­tion in­to lit­tle time, said bi­ol­o­gist Mi­chael H. Fer­kin of the Un­ivers­ity of Mem­phis, Tenn., the stu­dy’s lead au­thor.

Male voles seem to be aware of the females’ pat­tern of re­cep­ti­vity. 

In one ex­pe­ri­ment, Fer­kin and col­leagues briefly put male voles in a cage that con­tained two cham­bers. One cham­ber con­tained a fe­male that was a day away from giv­ing birth. The oth­er con­tained a fe­male that was sex­u­ally ma­ture, but not due to be in a state of height­ened re­cep­ti­vity an­y­time soon.

A day lat­er, the males were placed in the same ap­pa­rat­us, which was now emp­ty and clean. The males in­i­tially “chose and spent sig­nif­i­cantly more time in­ves­ti­gat­ing the cham­ber that orig­i­nally housed the preg­nant fe­ma­le”—who would by now have en­tered peak re­cep­ti­vity, the re­search­ers wrote.

This sug­gested, they continued, that the males both re­called and used key in­for­ma­tion from the ear­li­er event: what was in the cage, where and when.

Un­der slightly al­tered con­di­tions, male voles showed no pref­er­ence for ei­ther side of the cage, they wrote. For in­stance, when only half an hour had passed since the in­i­tial ex­po­sure to the fe­ma­les, there was no pref­er­ence ap­par­ent. Nor was there any in cases in which a day had passed, but where the in­i­tial en­coun­ter was dif­fer­ent—with a peak-re­cep­ti­vity fe­male re­plac­ing the preg­nant fe­ma­le. The peak-re­cep­ti­vity fe­male would no long­er be in that state a day lat­er.

“The re­sults of these and ad­di­tion­al ex­pe­ri­ments sug­gest that male voles may have the ca­pa­city to re­call the ‘what,’ ‘where,’ and ‘when’ of a sin­gle past event,” Fer­kin and col­leagues wrote in the pa­per, pub­lished in the jour­nal’s July 26 ad­vance on­line is­sue. This know­l­edge “may al­low males to re­mem­ber the loca­t­ion of fe­males who would cur­rently be in height­ened states of sex­u­al re­cep­ti­vity.”

The work “ap­pears to be a very thor­ough and care­fully done piece of re­search that makes a sol­id con­tri­bu­tion,” wrote psy­chol­o­gist Bill Roberts of the Un­ivers­ity of West­ern On­tar­i­o in Lon­don, On­tar­i­o, in an e­mail. “The con­trols used are im­pres­sive.” Roberts had ar­gued in a 2002 pa­per that re­search up to then sug­gested an­i­mals have no sense of time.

Fer­kin’s study does make at least one “ma­jor as­sump­tion,” Roberts added: that the males some­how know that the late-preg­nant fe­males will be re­cep­tive 24 hours lat­er. Anoth­er pos­si­ble problem, Fer­kin and col­leagues them­selves wrote, is that the ro­dents may just know how to make de­ci­sions based on how viv­id or faint a mem­o­ry is—with­out un­der­stand­ing that this de­pends on how much time has passed. In oth­er words, they might lack a real con­cept of time.

University of Tor­onto mem­ory re­search­er End­el Tulv­ing cited an­other, “mi­nor” quib­ble with the study. Voles have a very keen sense of smell, he noted. Per­haps—un­be­knownst to the hu­mans—even in cleaned, dis­in­fected cages, the ro­dents could sniff some­thing that cues their act­ions.

But overall, the find­ings add to a body of work sug­gesting an­i­mals have a ca­pa­city for “men­tal time trav­el,” Roberts wrote. For in­stance, past work sug­gested some apes can an­ti­cipate a fu­ture need for tools, and scrub jays re­mem­ber what kind of food they stored, where and when.

* * *

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A long string of experiments over decades have repeatedly found that animals aren’t as dumb as humans traditionally thought they were. Far from it. But are they really conscious? Studies have given only vague glimpses of an answer. But some scientists have said an organism must be conscious if it has “episodic memory”—basically the memory of the “what, where and when” of events in its life. New research has found that animals may have just this sort of memory. Rodents known as meadow voles can “recall the ‘what,’ ‘where,’ and ‘when’” of a past event, researchers wrote in the title of a new study published in the research journal Animal Cognition. Although past studies had suggested such abilities in animals, they involved putting the creatures through tests that involved some training, the authors said. That opened the results to criticism that the training could have affected their behavior in some way that made the animals merely act as though they knew “what, where and when.” The new study involved no pre-training. It exploited the fact that female voles, along with some other animals, enter a period of peak sexual receptivity just after giving birth. The somewhat surprising tendency may be explained by the creatures’ short lifespan, which compels them to pack a lot of reproduction into little time, said biologist Michael H. Ferkin of the University of Memphis, Tenn., the study’s lead author Male voles seem to be aware of this pattern of receptivity. In one experiment, Ferkin and colleagues briefly put male voles in a cage that contained two chambers. One chamber contained a female that was a day away from giving birth. The other contained a female that was sexually mature, but not due to be in a state of heightened receptivity anytime soon. A day later, the males were placed in the same apparatus, which was now empty and clean. The males initially “chose and spent significantly more time investigating the chamber that originally housed the pregnant female”—who would by now have entered peak receptivity, the researchers wrote. According to them, this suggested the males recalled what to them were the critical pieces of the earlier event: what was in the cage, where in the cage, and when. Under slightly altered conditions, male voles showed no preference for either side of the cage, they wrote. For instance, when only half an hour had passed since the initial exposure to the females, there was no preference apparent. Nor was there such in cases in which a day had passed, but where the initial encounter was different—with a peak-receptivity female replacing the pregnant female. The peak-receptivity female would no longer be in that state a day later. “The results of these and additional experiments suggest that male voles may have the capacity to recall the ‘what,’ ‘where,’ and ‘when’ of a single past event,” Ferkin and colleagues wrote in the paper, published in the journal’s July 26 advance online issue. That “may allow males to remember the location of females who would currently be in heightened states of sexual receptivity.” The work “appears to be a very thorough and carefully done piece of research that makes a solid contribution,” wrote psychologist Bill Roberts of the University of Western Ontario in London, Ontario, in an email. “The controls used are impressive.” Roberts had argued in a 2002 paper that research up to then suggested animals have no sense of time. Ferkin’s study does make at least one “major assumption” Roberts added: that the males somehow know that the late-pregnant females will be receptive 24 hours later. Another possible shortcoming, Ferkin and colleagues themselves wrote, is that the rodents may just know how to make decisions based on how vivid or faint a memory is—without understanding that depends on how much time has passed. In other words, they might have no real concept of time. The findings add to a body of work suggesting animals have a capacity for “mental time travel,” Roberts wrote. For instance, past work suggested some apes can anticipate a need for future tools, and scrub jays remember what kind of food they stored, where and when.