What is the link between autism and a lack of attachment between infant and parent?

We shall begin by examining the multidimensional nature of the attachment construct. As argued by Rutter [98], the concept of attachment has served to increase precision in the field, by translating the fuzzy notion of “love” into a measurable set of behavioral manifestations. Nevertheless, such manifestations include a range of different behaviors, including distress upon separation from the caregiver and selective proximity-seeking. The most influential operationalization of attachment is Ainsworth’s “strange situation” paradigm, which classifies attachment quality based on the child’s response to two episodes of separations from and reunion with the caregiver [1]. While originally conceived to provide a proxy for ordinary situations in which children seek the caregiver in order be soothed when upset, this protocol highlights one particular dimension of attachment, i.e., distress and proximity-seeking behaviors in response to stressors/threats. We will define this phenomenon as an ‘externally-driven’ attachment response.

Other conceptualizations of attachment, however, appear to reflect ‘internally-driven’ attachment responses, that is, selective proximity-seeking that occur in the absence of external threats or stressors. For example, the NIMH Research Domain Criteria (RDoC) matrix, a classification of biologically-based dimensional processes that are relevant to atypical development [49], identifies ‘Affiliation and Attachment’ as a unitary construct within the ‘Social Processes’ domain, according to the following definition “Affiliation is engagement in positive social interactions with other individuals. Attachment is selective affiliation as a consequence of the development of a social bond”. As we argue throughout the rest of the paper, consideration of both externally-driven and internally-driven dimensions of attachment might be critical to address the puzzle of attachment behavior in ASD.

“Autism” is the diagnostic concept originally articulated by Leo Kanner [55] to describe a clinical syndrome characterized by early emerging social communication abnormalities and behavioral rigidity. His emphasis on reduced social engagement, restricted/repetitive behaviors, and early onset of symptoms as the hallmarks of this condition has proven enduring, with current diagnostic definitions of ASD substantially adhering to Kanner’s diagnostic concepts [2].1 While engagement in restricted and repetitive behaviors can be observed across a number of disorders [12], the social reciprocity impairments originally described by Kanner are unique to ASD. Compared to typically developing children, children with ASD show fewer behaviors aimed at creating and maintaining social exchanges (e.g. vocalizing, mutual gaze, pointing to request or express interest, sharing emotions, showing objects to others, imitating, sharing attention, helping), as well as difficulties in understanding others’ communication and social cues. The centrality, earliness, and distinctiveness of these social impairments have lead scholars to view ASD as a disorder of social attachment since the early conceptualizations of this condition. For example, Mahler’s influential theory [67] posited that autism was caused by a pathological lack of child-caregiver attachment, whereby the child “devoid of emotional ties to the person of the mother, is unable to cope with external stimuli” [67], p. 682). The view that “unhealthy” parent-child attachment caused autism (explicitly endorsed by [14], p. 346) was later discredited, partly in response to emerging evidence that caregiving behavior in parents of children with ASD was indistinguishable from that of parents of children without ASD [27], [31]. Nevertheless, the notion of autism as a disorder characterized by lack of social attachment continued to be embraced in the following three decades, but this was based on the premise that symptoms of ASD were the cause of impaired attachment, rather than the other way around (e.g. [18], [96]). This notion is reflected in the current diagnostic definition of autism originally proposed in 1993 by the International Classification of Diseases (ICD-10; [130]), which lists, among other diagnostic criteria: “abnormal or impaired (…) development of selective social attachments”.

As the body of experimental research on attachment in ASD grew, the intuitive idea that the unique social reciprocity deficits defining this disorder must interfere with attachment formation turned out to be unsupported. The seminal study by Sigman and Ungerer [111] and subsequent research documented that ASD can, and in most cases does co-exist with secure attachment [17], [19], [32], [45], [58], [91], [92], [95], [94], [108], [110], [117], [118]. Key-findings from this body of literature include the following: 1) children with ASD respond preferentially to familiar people versus strangers (e.g. [56], 2) they seek proximity with caregivers after a separation in a way that in most cases does not differ from mental-age matched peers (e.g. [110], 3) the presence of a stranger causes children with ASD to engage in more proximity-seeking and less explorative behavior (e.g. [32], 4) when the quality of child-caregiver attachment relationship is assessed using the Strange Situation Procedure, the majority of children with ASD can be classified as having a “secure attachment” [94], 5) the proportion of children with ASD classified as having a “disorganized” attachment is higher compared to the normal population, but similar to mental-age matched children without ASD who have other (non-social) delays (e.g. [76]). Therefore, it appears that ASD does not preclude the establishment of secure social attachments. Importantly, this body of literature is based mostly on externally-driven attachment responses, i.e., behavioral manifestations of selective proximity-seeking that occur in response to stress/external threats.

At the same time a growing body of experimental research has pointed to the centrality of social motivation as a framework to describe and, according to some scholars, explain the core deficit of ASD [23], [30]. Specific findings supporting the “social motivation” theory of ASD include the following: 1) a lack of preferential orienting toward social stimuli (e.g. human faces and voices) versus non-social stimuli (e.g. geometric patterns, non-human noises), with diminished social attention manifesting as early as in the first six months of life [53], and interest in non-social stimuli in toddlerhood predicting the developmental of ASD symptoms [85], 2) diminished engagement in social and cooperative activities throughout the lifespan [65], [109], [123], and 3) decreased expressions of pleasure in social situations, suggesting that individuals with ASD do not experience social interactions as rewarding as typical peers do [22].2

The co-existence of such profound social abnormalities with intact social attachment (at least in its externally-driven dimension) poses a number of challenges, which we discuss in the following section.