Animal-Assisted Interventions; Effects on Human Mental Health - A Theoretical Framework

In the Western part of the word the public health challenges have changed dramatically during the last decades. Modern medicine and new technology has reduced mortality rates for most diseases and the life expectancy has increased. However, in the modern society of today, we face new threats to public health, mainly related to life style related diseases and illnesses such as obesity, diabetes, cardiovascular disease, musculoskeletal disorders and mental health problems. The prevalence of mental health problems is high and increasing, and previous epidemiological studies have estimated the lifetime prevalence of mental disorders to be approximately 50 % (Kringlen et al., 2001; Robins & Regier, 1991). Affective disorders are one of the most common mental disorders, and in a WHO survey from sixty countries, one-year prevalence for depressive disorders was 3.2 % (Moussavi et al., 2007). This is slightly lower than in a European survey, which estimated one-year prevalence for major depression to be 3.9 % (Alonso et al., 2004). In different surveys the lifetime prevalence varies from 8 to 18 % (Alonso et al., 2004; Kringlen et al., 2001, 2006). In a Norwegian study the diagnoses with the largest percentage increase in sickness absence the last decade were sleep problems, tiredness, anxiety (Ihlebaek et al., 2007), and today mental health problems account for almost 25% of new disability pension grants in Norway (Mykletun & Knudsen, 2009). In addition to individual suffering, this constitutes a major economical challenge to the society, as a review of Luppa et al. (2007) found that indirect economical costs, mainly due to sick leave and work disability, was twice as high as direct costs. Even though there has been substantial economical effort to develop and strengthen the traditional health care system for these problems, it does not seem to reduce the problem and still many patients do not get the treatment and rehabilitation they need. It is therefore necessarily to investigate other and complementary interventions and therapeutic approaches that might be useful. According to historical and prehistoric evidence, it is believed that the social symbiotic relationship between man and animal developed without any coercion from the human’s side (Odendaal, 2000). During the 20th century the introduction of animals to institutional care settings increased, and the concept of Animal-Assisted Therapy (AAT) was first mentioned by the child psychotherapist Boris Levinson (1962). Levinson described the


Introduction
In the Western part of the word the public health challenges have changed dramatically during the last decades.Modern medicine and new technology has reduced mortality rates for most diseases and the life expectancy has increased.However, in the modern society of today, we face new threats to public health, mainly related to life style related diseases and illnesses such as obesity, diabetes, cardiovascular disease, musculoskeletal disorders and mental health problems.The prevalence of mental health problems is high and increasing, and previous epidemiological studies have estimated the lifetime prevalence of mental disorders to be approximately 50 % (Kringlen et al., 2001;Robins & Regier, 1991).Affective disorders are one of the most common mental disorders, and in a WHO survey from sixty countries, one-year prevalence for depressive disorders was 3.2 % (Moussavi et al., 2007).This is slightly lower than in a European survey, which estimated one-year prevalence for major depression to be 3.9 % (Alonso et al., 2004).In different surveys the lifetime prevalence varies from 8 to 18 % (Alonso et al., 2004;Kringlen et al., 2001Kringlen et al., , 2006)).In a Norwegian study the diagnoses with the largest percentage increase in sickness absence the last decade were sleep problems, tiredness, anxiety (Ihlebaek et al., 2007), and today mental health problems account for almost 25% of new disability pension grants in Norway (Mykletun & Knudsen, 2009).In addition to individual suffering, this constitutes a major economical challenge to the society, as a review of Luppa et al. (2007) found that indirect economical costs, mainly due to sick leave and work disability, was twice as high as direct costs.Even though there has been substantial economical effort to develop and strengthen the traditional health care system for these problems, it does not seem to reduce the problem and still many patients do not get the treatment and rehabilitation they need.It is therefore necessarily to investigate other and complementary interventions and therapeutic approaches that might be useful.According to historical and prehistoric evidence, it is believed that the social symbiotic relationship between man and animal developed without any coercion from the human's side (Odendaal, 2000).During the 20 th century the introduction of animals to institutional care settings increased, and the concept of Animal-Assisted Therapy (AAT) was first mentioned by the child psychotherapist Boris Levinson (1962).Levinson described the 123 and measuring the effects of farm animals (including horses) on human mental health.Until now most of these studies are designed in the context of Green care.

Green care
Green care is an inclusive term for many complex interventions, such as social and therapeutic horticulture, animal-assisted therapy, care farming, green exercise, ecotherapy, wilderness therapy, e.g (Haubenhofer et al., 2010).Although there is much diversity under the umbrella of Green care, the term is grounded on the positive relationship between exposure of nature and human health (Sempik et al., 2010).Care farming (also called social farming or green care farming) is the use of commercial farms and agricultural landscapes as a base for promoting human mental and physical health, social inclusion and educational benefits through normal farm activity (Sempik, 2008).Most farms are ordinary family-based commercial farms, but also farms connected to health institutions and farms as part of therapeutic communities exist within Green care.Today the estimated number of Green care farms in Norway is 950 (Logstein & Bleksaune, 2010), and other European countries have similar figures (Haubenhofer et al., 2010).There is much variety among care farms, with differences in the extent of farm production or care, and in client groups.These may include patients with defined psychiatric diagnoses, people with learning disabilities, those with a drug history, disaffected youth or elderly people, as well as persons suffering from the effects of work-related stress or obesity.Many care farms offer contact with farm livestock (AAA), while others provide specific Animal-Assisted Therapy (AAT).Typically, the participants take part in the ordinary work tasks, like feeding animals, cleaning animals and the barn, milking cows, and they have the opportunity to pet and interact with the animals as much as they like.Although animal-assisted interventions with farm animals appear to be the most thoroughly studied type of Green care service, the evidence-based research is still scarce.

The human-animal relationship
Several authors have highlighted the association between people and animals, and provided some insights to this relationship.Tannenbaum (1995) claimed that the human-animal relationship need to be of a continuous nature and should be bi-directional and voluntary, while Russow (2002) claimed that the relationship must be reciprocal and persistent.She express further that there are no true relationship if the animal don't recognize you.However, it is not obvious that the human and the animal have a similar perception of their interaction.What a human experiences as pleasant, may be unpleasant for the animal.It has been known for many years that dogs and cats that have close contact with humans early in their lives are much friendlier to humans than animals that are exposed later on (Bateson, 1990).The restricted age-range within which such socialization is readily formed is known as the sensitive period for socialization, typically 3-12 weeks of age in dogs and cats.When this period starts, the animal is ready to form an attachment to a wide range of objects, but as it receives experiences with one object, it narrows its preferences to that one object.The consequence is that the animal is no longer able to enable new attachments.If the animal is exposed to several views of the same object while it is still narrowing its preferences, each of those views will be equally effective.Similarly, if the animal is exposed to different animals, including humans, it may form attachments to each of the objects, and the strength of the www.intechopen.comPsychiatric Disorders -Worldwide Advances 124 attachment will be related to the length of the exposure to the different individuals.When young animals are being exposed to several human individuals, the effect is more a general socialization on humans than attachment to a specific individual.If pet breeders do not give the young animals sufficient experience with humans, the animals will hardly function as pleasant, sociable pets.It is assumed that also farm animals should be socialized on humans in early life to function most effectively in animal-assisted interventions, and to avoid aggressive or fearful behaviour (Berget, 2006).Even without specific work on socialization, farm animals can usually be stroked, people can talk to them, and they may be good transitional beings like pets are.Katcher (2000) states that animals makes good transitional beings because they show intentional behaviour, they are capable of giving active affection, they can never contradict the attributes projected into them with words, and they can serve as vehicles for projection traits one might find lacking in human beings.According to Triebenbacher (1998) humans have an innate, biologically-based need for social interactions, and this interaction becomes increasingly focused toward specific persons.Behaviours such as following, smiling toward, holding and touching are evident in the relationship between child and attachment figures.Bowlby (1982) defined attachment as a form of behaviour in an individual seeking or maintaining proximity to another that serves as a secure base, and who is perceived as better able to cope with life stressors.Fundamentally this kind of attachment is found between a mother and offspring.To date theories of attachment used in research on human-animal relationships are based on theories applied on human-human relationships.Katcher and Beck (1989) recorded that a lot of persons appeared to have an attachment to their companion animals similar to that experienced with their friends and family, and Stallones et al. (1988) found that 95 % of elderly respondents regarded their companion animals as friends.In other studies, Cain (1983) and Voith (1985) found that a majority of the subjects regarded the pets as members of the family.Sife (1998) showed that as many as 70 % of people who share their lives with companion animals reported that they consider them as children.A similar study by Wallendorf and Belk (1987) documented that a majority of the respondents answered that their pets were substitutes for children, which may explain the tendency for people to use baby talk when speaking to their pets.Many human personality variables have been identified as being related to pet attachment.For example, people who had pets during childhood or adolescence tended to be more attached to their current pet than first-time caregivers (Kidd & Kidd, 1980), while the single adults tended to be more attached than the married adults.People who indicated a dog as their favourite pet tended to express a stronger attachment than those who reported a cat to be their favourite pet (Johnson et al., 1992).Crawford et al. (2006) examined if there were some common concepts between traditional attachment theory and human-animal attachment.The authors divided these aspects into among others; emotional bond, secure base, and representational models:

Emotional bond
According to Crawford et al. (2006), emotional bond is associated with closeness, frequency of petting or grooming one's animal, and levels of exercise.Enders-Slegers (2000) related emotional bond to caressing or holding an animal, or comfort derived from the relationship with the companion animal, while Odendaal (2000) claimed that the success of humananimal interaction is based on a two-way fulfilling of attention needs, and that the more social behaviour an animal exhibits, the more successful the bonding between human and animal can be.

Secure base
As earlier mentioned, the concept of secure base is fundamental in the field of attachment theory (Bowlby, 1988).The emotional security that pet owners report feeling in the relationship with their pets may in some ways parallel physical and emotional security as discussed within attachment theory (Triebenbacher, 1998).

Representation models
One's representational model of attachment often influences one's ability to deal with stressful life events (Bretherton, 1985).Similarly with traditional attachment theory, an individual's relationship with a companion animal may determine how well he or she will cope with stressful life events (Siegel, 1990).To summarize, attachment implies a long-lasting bond, and correlations between attachment and positive therapeutic outcomes have yet to be convincingly established in relation to human-animal relationship.In the context of AAI, the animal as a transitional object may appear to be more therapeutically desirable than that of an attachment figure (Katcher et al., 2000;Kruger & Serpell, 2006).

Animals as agents of socialization
In the late eighteenth century, theories concerning the socializing influence of animals began to apply to the treatment of mentally ill.In the Description of the Retreat, Samuel Tuke described how different animals, like rabbits, sea-gulls, hawks and poultry were a part of the milieu at the mental institution.The intention was that the interaction with the animals not only should give a means of innocent pleasure, but also to awaken the social and benevolent feelings (Serpell, 2010).

Animals as facilitators of social support
According to Cobb (1976) social support is defined as an interpersonal relationship that leads to "the persons believe in being cared for, loved, esteemed, and a member of a network of mutual obligations".Cobb suggested that social support that derives from a social relationship could provide protection from anxiety, depression and other related illnesses.This belief has been supported by research associated to mortality and morbidity of coronary heart disease (Eriksen, 1994), recovery of surgical procedures (Kulik & Mahler, 1989), and psychological well-being under stress (Winefield et al., 1992).The emotional support in initial stages of a severe stressor, like loss of functionality (Glass et al. 1993) and cancer diagnosis (Worthman, 1984), are also shown to be of importance for successfully coping with such stressors.Social support is an important part of mental health interventions as it could preserve feeling of self-esteem and sense of mastery (Milne, 1999).It is hypothesized that social support acting as a buffer against stress responses or illness can be derived not only from human relationships, but also from a human-animal relationship.According to McNicholas and Collis (2006) social support from pets may be a replacement for lacking human support, providing a release from relation obligations, enhance reorganization, re-establish routines, and "top up" existing human support.In a review of psychological, social, behavioural and physical benefits from pets with regard to social support, Garrity and Stallones (1998) found that pet association frequently appeared beneficial both directly and as a buffering factor during stressful life circumstances.In a study of horseback riding among children with mental and neuromuscular disabilities, Hart (1992) found that the intervention released joyous human social support as well as the unique sensation and physical challenge of riding a horse.Even the families of the affected children seemed to benefit.Appraisal support, with affirmation and feedback, is likely to be a part of the contact between the farmer and the participant in Green care.This was also found in the doctoral thesis of Pedersen (2011) on farm animal-assisted interventions for patients with a clinical depression.In addition to the accepting support the animal provided in her study, the participants expressed that they felt the farmer understood their situation and that they could easily express how they felt.Qualitative studies in The Netherlands (Elings & Hassink, 2008) and in Norway (Bjørgen & Johansen, 2007) have also emphasized the farmer contact and the social setting as important aspects for participants with mental health issues.An exploratory study at the Green Chimneys institution among 80 children with behavioural and mental health problems, showed that the children utilized the farm animals as if utilizing the service of a therapist; they visited the animals to feel better, and they learned about nutrition and caring for animals (Mallon, 1994).In a 12-week pilot project on AAI with goats for ten multiply-disabled adults (all deaf), the video registrations showed that the clients expressed joy and decreased withdrawal in contact with the goats.During the intervention the attentiveness and active participation increased.In contrast no such changes were found in a dining room situation on the residential institution for these persons (Scholl et al., 2008).

Animals as contributors to social contact
A mechanism often mention in the AAI literature is that animals may serve as catalysts or mediators of enhanced communication skills among people.The basis of this mechanism is that animals stimulate conversation by their presence and unscripted behaviour, and by providing a neutral, external subject on which to focus (Fine, 2000;Levinson, 1969).One of the first to evaluate the effects of pets as social catalysts in institutional settings was Corson et al. (1977).They focused on patients who did not respond sufficiently on traditional therapy.However, they failed to find a proper control group, and allowed the experimental group to act as their own controls in an intervention either with a dog in a kennel, on the ward, or at the patients' bedsides.The study showed that the pets and the patients enjoyed much time together, and analyses of videotapes showed that the patients appeared less withdrawn, and communicated more with the therapist.Another study in the early period was the study of Beck et al. (1986) comparing psychiatric inpatients in a room with caged birds with a similar patient group without any animals.The authors concluded that the patients in the room with the birds communicated more, and were more comfortable in communication than the controls.A study by Messent (1983) showed that dog owners walking in a park experienced a significantly higher number of chance conversations with other park users than when walking the same route without the dog.The study also demonstrated that the conversations were significantly longer when the dog was present.The presence of a dog acted as an ice breaker, providing a neutral and safe opening for conversation.A similar study by McNicholas & Collis (2000) showed that being accompanied by a dog in daily routines such as taking children to school, on public transport, for example, led to an increased number of conversations between people.However, the length of interactions did not increase, and the study demonstrated that the nature of the interaction depended on the relationship between the participants.The effects of the dog as a social catalyst were largest with strangers and smallest with friends.Another study by Bernstein et al. (2000) demonstrated that geriatric persons subjected to AAT were more likely to initiate and participate in longer conversations than a control group getting Non-Animal Therapy (NAT) like arts, crafts and snack bingo.Similar effects were found in a 12-month controlled study of elderly schizophrenic patients where contact with a pet, either a dog or a cat, resulted in significantly improved conversational and social skills in the experimental group compared with the controls (Barak et al., 2001).In a recently randomized controlled trial (RTC) with or without a dog among 24 patients with schizophrenia, Villata-Gil et al. ( 2009) found significant change in social contact and social relationship in the dog group.However, there were no significant differences in the outcome measures when comparing the two groups.Rosetti & King (2010) found in a review of AAT among a heterogeneous sample of psychiatric patients that AAT can improve socialization.To sum up, positive connections to enhanced social interaction were seen.However, from surveys with pet owners, positive connections to pets as social catalysts are not consistent (Pachana et al., 2005;Parslow et al., 2005).

Animals as contributors to reduced arousal, anxiety, and depression
The statement that animals are able to induce and mediate physiologically de-arousing effects, was first forwarded by Edward O. Wilson in his book Biophilia (1984).He defined biophilia as humans' natural tendency to focus on life and lifelike processes.This is not single instinct, but complex learning rules which could form a range of emotions like attraction and peacefulness, but also aversion and anxiety (Wilson, 1993).This tendency gave distinctive advantages in human evolution, and therefore there is partly a genetic basis for this positive responsiveness to nature (Kellert, 1993).This hereditary trait is utilized in different forms of nature-assisted therapy, which is documented to be effective for a diversity of diagnoses, such as obesity, schizophrenia and stress related disorders (Annerstedt & Währborg, 2011).The stress reducing effect of outdoor recreation and natural settings are extensively investigated and Ulrich (1993) emphasizes a probable relationship between nature, reduced stress and health.This stress recovery response is also much used as a potential mechanism of the observed health effects in companion animal research.A decline in blood pressure and heart rate are seen in several studies when people interact and have physical contact with a pet animal.The first published report on effects of companion animals on physical health was made by Erika Friedmann et al. (1980).This report showed a relationship between owning a dog or cat and increased probability of survival one year after heart attacks, myocardial infarctions or severe angina pectoris.While 28 % of nonowners died within one year, only 5.7% of pet owners died.Later research has confirmed this finding (Friedmann & Thomas, 1995).The increased survival could not be related to differences in seriousness of the attack, psychological or social status, or demographic variables.Stress-reducing effects of watching fish in an aquarium have been shown in www.intechopen.comPsychiatric Disorders -Worldwide Advances 128 several studies (e.g.Katcher et al. 1983).The same parasympathetic effects apply to watching animals of other species that people trust, while the opposite may be found for watching threatening animals.Interaction with a companion animal is also related to increased parasympathetic nervous activity (Matsuura et al., 2007), and increased level of salivary amylase activity which is associated with improvement of the immune function.Positive physical contact between humans like nursing a baby, or stroking, caressing or massaging between adults, may release the hormone oxytocin which is produced in the hypothalamus (Uvnäs-Moberg, 1998).General effects of oxytocin are relaxation and reduced stress level.Oxytocin coordinates both the causes and the effects of positive social interactions, and it can be conditioned to the psychological state or imagery of people.An increase in the beneficial hormone oxytocin is also observed when humans interact with pet animals (Handlin, 2010;Miller et al., 2009;Odendaal & Meintjes, 2003).In the PhD-thesis of Handlin (2010), ten female dog owners and their male Labrador dogs participated together with ten controls.Their levels of oxytocin, cortisol and insulin, as well as their heart rate, were measured.The connection between the quality of the dog-owner relationship and hormone levels was also explored.The short-term interaction between the dogs and their owners resulted in oxytocin release in both species, and the oxytocin levels and positive attitudes regarding the dog-owner relationship were positively correlated.In conclusion the study showed that the interaction with the dog induced oxytocin release, and promoted oxytocin mediated effects, such as decreasing cortisol levels and blood pressure.Other intervention studies with companion animals have shown a decrease in levels of stress hormones like adrenalin and noradrenalin (Barker et al., 2005;Odendaal, 2000).Several studies of AAIs with companion animals have examined the connection between changes in physiological measures and reduced state anxiety (Barker et al. 2003a,b;Cole et al., 2007;Hoffmann et al., 2009).There are only a few studies that have examined whether a decrease in anxiety are valid also for interaction with farm animals.However, Berget et al. (2011) found a decline in state anxiety at follow-up six months after the end of a threemonth intervention with farm animals for the intervention group of 41 participants with various psychiatric diagnoses (schizophrenia and schizotypal disorders, affective disorders, anxiety and stress-related disorders, and disorders of adult personality and behaviour) compared with the control group, as measured by Spielberger State-Trait Anxiety Inventory (state subscale, STAI-SS).Among the studied diagnoses, beneficial effects on anxiety tended to be higher among the persons with affective disorders.Among clinically depressed persons, Pedersen (2011) found a significant association between a high frequency of complex work tasks with dairy cattle and a decline in state anxiety (STAI-SS) during a 12week intervention.Complementary and supplementary treatments are widely used in treatment of depression.More than 50 % of people with depression reported using complementary treatment alone or together with conventional treatment in the US (Kessler et al. 2001).The reasons for this use are several; the side effects of medication are for many people difficult to accept, and a negative view of drug treatment in general could act as an incitement to use complementary treatments.Contact with pet animals is seen to be beneficial for mental health and depression.Souter and Miller (2007) conducted a meta-analysis to determine the effectiveness of AAT and AAA for reducing depressive symptoms in humans.Only five studies, all using dogs, were identified.The mean effect size for the sample of studies was statistically significant, and the findings supported the hypothesis that AAA and AAT are effective at alleviating depression.A more comprehensive meta-analysis was conducted by Nimer and Lundahl (2007) identifying 49 studies that met the inclusion criteria.The outcomes in the following four areas were studied; medical difficulties, autism-spectrum symptoms, behavioural problems, and emotional well-being.All studies identified moderate effect sizes in the improving outcomes, but research gaps on AAA and AAT were revealed.Previous controlled studies of interaction with pets have shown significant decrease in depression during one week of hospitalisation among 230 psychiatric patients with psychotic and mood disorders (Barker and Dawson, 1998) and after two weeks of intervention with dolphins (Antonioli and Riveley, 2005).In a controlled pilot study on the effect of AAT on anhedonia among 10 schizophrenic patients, the Snaith-Hamilton Pleasure Scale showed significant improvement in the AAT group with a dog compared with the controls (Nathans- Barel et al., 2005).A few studies point to a reduction in depression among persons working with farm animals (Berget et al., 2011;Hine et al., 2008;Ketelaars et al., 2001;Pedersen, 2011).However, for some persons this is only evident during the follow-up period (Berget et al., 2011) or for those that acquire more complex working skills (Pedersen, 2011).Reduction in depression was also found in the control group, although to a lower degree.

Animals as facilitators of self-efficacy and self-esteem
Based on social cognitive theory, there is a continuous relationship between a person's cognition, behaviour and environment, and the goal of therapy is to bring about positive changes in a person's self-perception and hence their behaviour by improvements in selfefficacy, self-esteem and locus of control.Perceived self-efficacy is a major determinant of motivation for and choice of activity.It also affects the amount and duration of effort a person will allocate in order to cope in a situation or with a task.According to Albert Bandura (1977) self-efficacy is concerned with judgments of how well one can execute courses of action required to deal with prospective situations.People avoid activities that they believe exceed their coping capacities, but they undertake and perform assuredly those that they judge themselves capable of managing.People with low self-efficacy avoid difficult tasks, they lower their goals, and seek less support from others.Failures make them lose faith in themselves, and in turn contribute to lowered mood and depression (Bandura, 1982(Bandura, , 1986(Bandura, , 1997)).Benefits of AAI is often ascribed as the ability of animals to act as living, interactive tools that can be used to help people see both themselves and the world in new ways, and add new skills and responses to their behavioural repertoires (Nebbe, 2000).Although there is some overlap between these theories and those described in the previous sections, what sets them apart is their emphasis on the formation of a working relation between the client and the animal.Most programs that incorporate equines and animal training and care-taking, draw heavily from these theories.There are to date few long-term follow-up studies of the impact of AAI with companion animals on self-efficacy and self-esteem.However, previous RTC-studies with farm animals for severely diseased psychiatric patients showed an increase in self-efficacy at follow-up six months after the end of a three-month intervention for the treatment group, but not for the controls (Berget et al., 2008a;Pedersen, 2011).The studies indicate that positive effects of animal interventions on self-efficacy among these patient groups may take a long time to develop.However, according to Kruger & Serpell (2010), theories that enhance behaviour changes beyond the context of a working relationship with an animal are conflicting, and yet no evidence exist that longstanding benefits are derived from participation in such programs.

Attitudes to Animal-Assisted Interventions among therapists
There are until now a few studies examining the attitudes of AAIs among different groups of health care personnel.A study of Rice et al. (1973) showed that that the therapists utilized pets as vehicles for cultivating or modelling the positive nature of interpersonal relationship, and most of the 40 respondents pointed out that animals were used to ease the stress of the initial phase of therapy to establish rapport.A qualitative study among 13 psychotherapists using AAT with dogs, found that the majority of the therapists ranked anxiety disorders as one of the diagnoses that profited most on AAT (Mason & Hagan, 1999).Another study by Berget et al. (2008b) examining 60 psychiatric therapists' knowledge, experience and attitudes to Green care and AAT with farm animals for people with psychiatric disorders, showed that most of the therapists thought that AAT with farm animals contributed to increased skills in interactions with other humans.Two-thirds of the therapists believed that AAT with farm animals to a large extent could contribute better to mental health than other types of occupational therapy.However there were no differences in attitudes to AAT between the different professions.A recent survey of beliefs in treatment effects of AAIs for psychiatric patients among 1100 Norwegian practitioners found that the therapists beliefs in treatment effects were most significant for better physical conditions, less symptoms (e.g.anxiety, depression), and a better ability to cope in daily life.The strongest degree of usefulness was reported for mental retardation, while the least significant one was for schizophrenia disorders.Women, more than men, believed in treatment effects and those with a professional experience with AAI more than those without the same experience.Finally, the beliefs in treatment effects from pets were slightly higher than those for farm animals (Berget & Grepperud, 2011).Future evidence-based studies with AAIs in different therapeutic settings will be of importance to develop more professional standards of practise, achieve additional credibility, and become recognized as a legitimate and multidisciplinary speciality.Also studies to investigate effects of AAI's in combination with different rehabilitation programs need to be explored.

What kind of species is preferred in AAIs?
Selection of species and type of animal used in AAIs are important in order to obtain the desired outcome.People, who are burdened due to difficult personal circumstances or poor health status, as is common for the elderly, can benefit from choosing a cat that requires less care than a dog or a horse.For people with mental health problems a new branch of AAIs using horses is recently evolving; equine-facilitated psychotherapy (EFP).EFP is an experiential psychotherapy that includes equines, and is facilitated by a licensed credentialed mental health professional together with an appropriately credentialed equine professional.EFP may include handling, grooming, longeing, riding, driving and vaulting (Equine Facilitated Mental Health Association, 2010).Green Chimneys (2010) is an example of a comprehensive residential treatment centre for mentally disturbed children where EFP is one of the important treatment modalities that are available.One difference in using e.g.dogs and horses as complementary treatments is whereas dogs can be available 24 hours a day to provide companionship and comfort, EFP requires a significant infrastructure and human organization in order to provide treatment.Previous studies have demonstrated that EFP is uniquely effective in motivating psychiatric patients and facilitating treatment (Bizub et al., 2003;Burgon, 2003;Fitzpatrick & Tebay, 1997).Similar findings are also shown in studies with traditionally farm animal species (dairy cattle, beef cattle, sheep and goats) (Berget et al., 2007;Scholl et al., 2008, Pedersen et al., in press).However, Cawley et al. (1994) did not reveal any benefits from an eight-week intervention with a horseback-riding programme on self-conception among adolescents with special educational needs.To sum up, a variety of animal species can be used in AAIs, but it is recommended to restrict them to domesticated species, partly by considerations of the safety of the participants, and partly in order to ensure adequate animal welfare.The most feasible species are therefore companion animals, horses and farm animals.

Summary and conclusions
The prevalence of mental health problems is high and increasing.Many patients experience that they might not receive satisfactory treatment and rehabilitation in the traditional health care system, and it is therefore necessarily to investigate other and complementary interventions and therapeutic approaches.One such complementary intervention is AAI, with growing evidence of beneficial effects.The relationship between people and animals is complex, and should always be bi-directional and voluntary.Processes of human-animal interactions may partly be explained by a number of different models or theories, and most of these are based on theories developed for human-human relationships which are applied for human-animal relationships.These theories are not mutually exclusive; and probably there will be large individual differences in which theoretical framework that are most useful and adequate.There are several common concepts between Bowlby's traditional attachment theory and human-animal attachment, and it is hypothesized that animals could play an important role in creating emotional bonds, provide a secure base, and to assist in building representational models.Another theory is social support, and pets may offer a substitute for lacking human support, and thereby acting as a buffer against stress responses or illness.Furthermore, studies show that pets often acts as catalysts facilitating social contact between humans.The theory of biophilia emphasizes that humans through evolution have a natural tendency to focus on nature and life, and as a consequence there are beneficial relationship between nature, reduced stress and health.A release of the hormone oxytocin and decline in blood pressure and heart rate, are seen in several studies when people interact and have physical contact with a pet animal, and this might explain the reduced arousal, anxiety, and depression reported in several studies on AAI.Yet another relevant theoretical framework is Bandura's model of self-efficacy, and animals can be seen as living, interactive tools that can be used to help people add new skills and develop coping abilities.Even though several theories have been proposed, the theoretical framework of AAI is still insufficient.New theories should be developed that generate testable predictions of specific effects of human-animal interactions.