Brain Research on Fully Conscious Macaques

Left: Experiment performed by Lawrence Pinneo of Tulane University, similar to the macaque brain experiments at the University of Toronto. The researcher is able to make the monkey move by stimulating parts of the brain. Photographs and video footage of the experiments at the University of Toronto have not yet been released.

Researchers at the University of Toronto Faculty of Dentistry have been conducting brain research on fully conscious macaque monkeys for almost 20 years.

The researchers surgically implant a stainless steel cylinder into each monkey's head (1982) (two cylinders, in some cases) (1999a, 1999b, 1998, 1997b, 1992b, 1992c, 1991, 1988). In at least some of the experiments, a "headcap of dental acrylic was fixed to the skull" as well (1999a, 1999b, 1998, 1997b, 1992a, 1992b, 1991, 1982). One journal article mentions that the headcap held a brass bolt 1 cm (about 1/2 inch) across which was used to hold the head still (1991). Then they insert small electrodes into the cortex of the brain and apply an electric current (1999a, 1999b, 1997b, 1992a, 1991, 1988, 1982). Depending on the part of the brain stimulated, this sometimes results in the monkeys' muscles moving against their will (1999a, 1999b, 1997b, 1992a, 1988, 1982).

By observation, and through more electrodes implanted in the monkeys' muscles (1999a, 1999b, 1998, 1997b, 1992a, 1992b, 1992c, 1991, 1988, 1982), the researchers determine which parts of the brain are used to move which muscles. When muscle movement occurs, according to one article, the researchers would then lower and raise the current to determine the minimum current necessary to get a response (1988). In recent years, the focus has been on movements of the mouth (chewing, swallowing, biting, sticking out the tongue) (1999a, 1999b, 1997b, 1992a, 1991, 1988), although in the past other movements of the face, and movements of the limbs, have also been investigated (1982).

In some experiments, parts of the brain were cooled (to 0-4 °C (1999b) or 2-4 °C (1998), 1991). The researchers observed that this significantly interfered with the monkeys' ability to chew (1998), swallow (1999b), and stick out their tongues (1991).

In at least one publication (1999a), the researchers acknowledge that data on areas of the brain involved in chewing and swallowing is already available from studies of human volunteers who have had strokes.

In some experiments, the researchers also touched the monkeys' faces and mouths with cotton swabs, their fingertips, and probes, and recorded any resulting activity in the brain (1999a, 1997b, 1992c).

During these experiments, the fully conscious monkeys are seated in "primate chairs" (1999a, 1994, 1992a, 1992b, 1992c, 1991, 1988, 1982). Their heads are held firmly in position by "headholders" (1999a, 1988, 1982). In at least one experiment, the monkeys were restrained by a chest plate taped to the chair and tape around one or both wrists (1982).

In some of the experiments, the monkeys were trained to bite or stick out their tongues in response to a computer signal. (1997b, 1994, 1992b, 1992c, 1991). To motivate them to learn these tasks, the monkeys' access to water was restricted to as little as "two-thirds of the normal daily intake" (1992b, 1992c, 1991) (except on weekends, when water was freely available). They were rewarded with fruit juice (1997b, 1992b) for biting or sticking out their tongues when signalled.

In another experiment, the monkeys' teeth were fitted with different kinds of braces. Permanently implanted electrodes measured the effects on muscle activity when swallowing (1997a).

At the end of some of the experiments, the monkeys are killed (1999a, 1992a, 1991, 1988, 1982). In other cases, the same monkeys are reused in a series of experiments spanning years, e.g. the monkeys named H5 and H6 (1998, 1994, 1992a, 1992b, 1992c, 1991).

One article mentions that the ages of the two monkeys used were "established by charts that relate the dentition to age in nonhuman primates" (1997a), suggesting that these monkeys may have been caught in the wild rather than born in captivity.

Some recent experiments were videotaped (1999a, 1992b, 1992c). Freedom for Animals is asking that these videotapes (and any others of these experiments) be released to the public.

References

These are only some of the published macaque brain experiments. More will be added to this list by our all-volunteer staff as time permits.

1999a: Ruth E. Martin (University of Western Ontario), Pentti Kemppainen (University of Helsinki), Yuji Masuda (Osaka University), Dongyuan Yao (former grad student), Gregory M. Murray (former grad student, now at the University of Sydney), and Barry J. Sessle. Features of cortically evoked swallowing in the awake primate (Macaca fascicularis). Journal of Neurophysiology. 82(3):1529-41. Funded by Canadian taxpayers (Canadian Medical Research Council Grant MT-4918) and Ontario taxpayers (Ontario Ministry of Health Career Scientist Award to Ruth E. Martin). This experiment used two macaques (named H7 and H8) for 11 and 13 months respectively. 1,569 different sites in their brains were stimulated.

1999b: Noriyuki Narita (Nihon University), Kensuke Yamamura (Niigata University), Dongyuan Yao (former grad student), Ruth E. Martin (University of Western Ontario), and Barry J. Sessle. Effects of functional disruption of lateral pericentral cerebral cortex on primate swallowing. Brain Research. 824(1999):140-145. Funded by Canadian taxpayers (Medical Research Council grant MT-4918 to Barry J. Sessle, and MRC fellowship to Dongyuan Yao). This experiment used two macaques.

1998: Li-Deh Lin (former grad student, now at National Taiwan University), Gregory M. Murray (former grad student, now at University of Sydney), and Barry J. Sessle. Effects on non-human primate mastication of reversible inactivation by cooling of the face primary somatosensory cortex. Archives of Oral Biology. 43(1998):133-141. Funded by Canadian taxpayers (Medical Research Council grant MT-4918 to Barry J. Sessle). This experiment used two macaques (named H5 and H6).

1997a: Camilo Yamin-Lacouture, Donald G. Woodside, Pavel A. Sectakof, and Barry J. Sessle. The action of three types of functional appliances on the activity of the masticatory muscles. American Journal of Orthodontics and Dentofacial Orthopedics. 112:560-572. Funded by Canadian taxpayers (Canadian Medical Research Council grant MT-4918). This experiment used eight macaques.

1997b: Ruth E. Martin (University of Western Ontario), Gregory M. Murray (former grad student, now at University of Sydney), Pentti Kemppainen (University of Helsinki), Yuji Masuda (Osaka University), and Barry J. Sessle. Functional properties of neurons in the primate tongue primary motor cortex during swallowing. Journal of Neurophysiology. 78: 1516-1530. Funded by Canadian taxpayers (Medical Research Council Grant MT-4918 to Sessle), Ontario taxpayers (Ontario Ministry of Health Career Scientist Award to Martin), and Medical Research Council of the Academy of Finland award to Kemppainen. This experiment used two macaques (named H5 and H7).

1994: Ekram Mahmoud Moustafa (former grad student), Li-Deh Lin (former grad student, now at National Taiwan University), Gregory M. Murray (former grad student, now at University of Sydney) and Barry J. Sessle. An electromyographic analysis of orofacial motor activities during trained tongue-protrusion and biting tasks in monkeys. Archives of Oral Biology. 39(11):955-965. Funded by United States taxpayers (National Institutes of Health grant DE04786). This experiment used two macaques (named H5 and H6) over a period of one year (spread out over seven sessions with 6 to 8 weeks between each session).

1993: Li-Deh Lin (former grad student), Gregory M. Murray (former grad student, now at University of Sydney) and Barry J. Sessle. The effect of bilateral cold block of the primate face primary somatosensory cortex on the performance of trained tongue-protrusion task and biting tasks. Journal of Neurophysiology. 70(3):985-996. Funded by Canadian taxpayers (Medical Research Council grant MT-4918 to Sessle). This experiment used two macaques (named H5 and H6).

1992a: Gregory M. Murray (former grad student, now at the University of Sydney) and Barry J. Sessle. Functional properties of single neurons in the face primary motor cortex of the primate. I. Input and output features of tongue motor cortex. Journal of Neurophysiology. 67(3):747-758. Funded by Canadian taxpayers (Medical Research Council grant MT4918 to Barry Sessle and fellowship to Gregory Murray). This experiment used two macaques (named H5 and H6). 133 sites in their brains were stimulated.

1992b: Gregory M. Murray (former grad student, now at the University of Sydney) and Barry J. Sessle. Functional properties of single neurons in the face primary motor cortex of the primate. II. Relations with trained orofacial behaviour. Journal of Neurophysiology. 67(3):759-774. Funded by Canadian taxpayers (Medical Research Council grant MT4918 to Barry Sessle and fellowship to Gregory Murray). This experiment used two macaques (named H5 and H6).

1992c: Gregory M. Murray (University of Sydney) and Barry J. Sessle. Functional properties of single neurons in the face primary motor cortex of the primate. III. Relations with different directions of trained tongue protrusion. Journal of Neurophysiology. 67(3):775-785. Funded by Canadian taxpayers (Medical Research Council grant MT-4918 to Barry J. Sessle and fellowship to Gregory M. Murray). This experiment used two macaques (named H5 and H6).

1991: Gregory M. Murray (former grad student, now at the University of Sydney), Li-Deh Lin (former grad student), Ekram Mahmoud Moustafa (former grad student), and Barry J. Sessle. Effects of reversible inactivation by cooling of the primate face motor cortex on the performance of a trained tongue-protrusion task and a trained biting task. Journal of Neurophysiology. 65(3):511-530. Funded by Canadian taxpayers (Medical Research Council MT-4918 to Sessle and fellowship to Murray). This experiment used two macaques (named H5 and H6).

1988: Chiung-Shing Huang (former grad student), M. A. Sirisko, H. Hiraba, Gregory M. Murray (former grad student, now at the University of Sydney) and Barry J. Sessle. Organization of the primate face motor cortex as revealed by intracortical microstimulation and electrophysiological identification of afferent inputs and corticobulbar projections. Journal of Neurophysiology. 59(3):796-818. Funded by Canadian taxpayers (Medical Research Council grant MT-4918). This experiment used 10 macaques for two to 15 weeks. 29,102 sites in their brains were stimulated.

1989: Chiung-Shing Huang (former grad student), H. Hiraba (Nihon University), and Barry J. Sessle. Input-output relationships of the primary face motor cortex in the monkey (Macaca fascicularis). Journal of Neurophysiology. 61(2):1989. Funded by Canadian taxpayers (Medical Research Council grant MT-4918 to Sessle). This experiment used two monkeys (named H3 and H4).

1982: Barry J. Sessle and M. Wiesendanger (Université de Fribourg, Switzerland). Structural and functional definition of the motor cortex in the monkey (Macaca fascicularis). Journal of Physiology 323:245-265. Funded by Canadian taxpayers (Canadian Medical Research Council Grant MT-4918) and the Swiss Science Foundation Grant 3.266-0.77. This experiment used three macaques over a period of two to eight weeks. Almost 5,000 different sites in their brains were stimulated.

Last updated April 11, 2002.