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Supportive Findings From Nonhuman Animal Studies A number of ablation, stimulation, and direct cell recording studies have corroborated evidence for the function proposed by research using humans. In rhesus macaque monkeys, for instance, electrical stimulation of the cingulate cortex has been shown to produce a range of vocalizations and facial expressions, accompanied by autonomic changes such as increased heart rate, respiration, and blood pressure. More refined evidence comes from individual cell recordings in monkeys. This data shows activation within the ACC during error monitoring, response, and prediction during working memory tasks. Much of the research using monkey trials has provided support for the ACC's involvement in error monitoring and reward processing. This remains perhaps the most studied function of the ACC, likely due in part to the fact that error monitoring trials are much more easily designed using nonhuman animals than higher cognitive functions that require feedback from the participant with regard to what they are thinking or feeling.

However, other research has been carried out assessing more natural behaviors among lesioned animals. Ablation studies with monkeys have shown that placidity and decreased aggression occur following lesions in this region (a finding contradictory to the behavior of lesioned cats, as explained below). In one study, monkeys were lesioned in the area of the anterior cingulate gyrus with limited inclusion of neighboring regions, then monitored for a number of weeks for alterations in behavior. Glees and colleagues found a loss in the sense of danger in 5 out of the 7 monkeys used. They also reported an increase in tameness and a decrease in aggression. However, these results were not permanent, and within weeks the behavior had returned to a more normal state. These results were used as rationale for lesioning the same region in humans in an attempt to decrease aggressiveness in those with "distorted personalities."

Conversely, one ablation study in cats induced rage behavior and other anomalies. In this study, a group of cats had what was believed to be their cingulate cortex destroyed. However, the authors expressed difficulty in identifying specific regions due to anatomical differences in the cat brain. Following the ablation, behavioral changes tended toward automatic, repetitive, slow movements that did not seem to be aligned with the animal's present reality. For example, cats would walk through food and water without seeming to notice what it was they were walking through. Furthermore, many of the cats would not respond to food until having their head forced into it, at which point they would lap up all of the food present and continue lapping even after the last of the food was gone. Significant emotional variation also occurred, where cats who had been kept together and who had played together would exhibit what the authors describe as "rage" phenomena toward the other following the surgery. Cats also demonstrated abnormally constant purring. Another key finding of cingulate ablation from Kennard et al. was the impairment of complex motor behaviors and the tendency to remain stuck in "bizarre" positions. Some of these altered behaviors faded, though the authors report no reduction in the rage behavior, as was seen in monkeys.

These studies provide neuropsychological results for the motor, emotional, and error-related function of the ACC in mammals, similar to those found in humans. However, the rage behavior found in cats does not fit with the prevailing evidence from primate studies. As was seen in monkeys, aggressiveness decreased. In humans, destruction of this region has led, among other things, to the effect of akinetic mutism described above. Naturally, effects on phenomena like the sense of will, again related to akinetic mutism, is much more difficult to study in nonhuman animals. With that said, the lethargy and placidity described as tameness by Glees and colleagues appears similar to the lack of behavior seen in those with akinetic mutism, if to a far lesser degree.

Spindle Cells in Nonhuman Animals Spindle cells (also known as Von Economo neurons) are characteristic for both their cell body volume and their length, and are uniquely prevalent within the ACC. In humans, spindle cell bodies within layer V of the cortex are four times larger than the surrounding pyramidal cells, and the length of the cell is thought to allow for fast transmission of information over relatively long distances within the cortex. Within the other great apes, cell volume and prevalence decrease with phylogenetic distance from humans. Strong spindle cell connections are found between the frontoinsular cortex and the ACC in humans, and have been found in neighboring areas, but are not present in any other part of the brain. Consequently, these cells are believed to have evolved from evolutionary pressures of large brains and complex cognition, particularly social cognition. This theory is supported by the animals they have so far been discovered in: elephants, some cetaceans, and the great apes.

It was originally thought that only great apes (humans, chimpanzees, orangutans, & gorillas) possessed spindle cells. However, it seems that other species that display complex social cognition, such as elephants and dolphins, also develop these distinctive neurons. In fact, the "cell that makes us human," as they have been described, are found with comparable prevalence in some cetaceans, such as orcas and bottlenose dolphins. Cetaceans began an evolutionary path separate from humans about 55 million years ago, yet these neurons only appear to have developed in primates 15-20 million years ago, which would make this a case of convergent evolution. This supports the theory that they are necessary for large brains with demanding social needs, as cetaceans are among the most social species in the world. Further support would be gained from an analysis of other large, though less social, animals, such as the giraffe or hippopotamus.

The unique prevalence of these cells in the ACC, and their limitation to animals of complex social behavior, has been widely interpreted as supporting evidence for the role of this region in social awareness that would entail quick decisions based on complex social situations. The combination of histological assessment of spindle cell prevalence in these species, lesion studies and direct recordings in monkeys and cats, and human behavioral data, lend converging evidence to many of the functions proposed above.