Disorganized Attachment pattern affects the perception of Affective Touch

Touch, such as affective caress, can be interpreted as being pleasant. The emotional valence that is assigned to touch is related to certain bottom-up factors, such as the optimal activation of C-tactile (CT) afferents. Tactile processing with a hedonic or emotional component has been defined as affective touch—a component that CT fibers are likely to convey. Tactile deficiencies are frequent in the psychiatric population but also in healthy people with disorganized attachment; accordingly, it is likely that affective difficulties in adults with disorganized attachment are reflected in altered perception of affective touch. To test this hypothesis, we combined methods from clinical psychology, psychophysics, and neuroimaging. We found that people with a history of traumatic parental bonds and a disorganized attachment pattern perceive a “caress-like” stimulus as being unpleasant, whereas participants with organized attachment consider the same tactile stimulation to be pleasant. Further, unlike in organized adults, the responses of disorganized adults to CT and non-CT stimulation activated limbic and paralimbic structures in a fight-or-flight manner, suggesting that early experiences with parental deficiencies shape the physiological responses of peripheral CT fibers and central nervous networks.


Adult Attachment Interview
The Adult Attachment Interview (AAI) [1] is a semi-structured, clinical interview designed to assess an individual's current state of mind with respect to past caregiver-child attachmentrelated experiences [2]. Interpretations of the adult attachment categories do not rely on the assumption that they represent veridical accounts of early childhood experience; rather, transcripts of the interviews are coded by trained raters according to how coherently people recall their past experiences. The individual's strategy during the AAI (e.g., derogating or minimizing of attachment vs. valuing and rendering a balanced, coherent narrative despite positivity or negativity of actual experience) is supposed to reflect the quality or security of one's current state of mind with respect to attachment [2]. Typically, one out of three possible main classifications is assigned to the most prominent state of mind throughout the interview as a whole: secure/autonomous (F), insecuredismissing (Ds), or insecure-preoccupied (E), of which secure/autonomous is considered the most beneficial. Furthermore, when present, discussions of experiences of loss, abuse, or other potential trauma are scored for disorientation in reasoning or discourse and, when sufficiently marked, may lead to a primary classification of a disorganized/unresolved (Ud) state of mind. In such a case, a secondary (organized) classification of secure/autonomous, insecure/dismissing, or insecure/preoccupied is assigned for the remaining narrative. Interviews in which a singular organized state of mind cannot be identified (e.g., because marked indications of several states of mind are present) are coded as cannot classify (CC) [3]. The AAIs were transcribed verbatim, and identifying information was removed prior to coding. To assess individual differences in attachment, transcripts were coded by a certified AAI coder, who had achieved greater than 80% agreement with on the official reliability test.  [11].

Tactile assessment
Von Frey Monofilaments. In this test, the tip of a fiber with a specific weight (from 0.008 to 300 g) is pressed against the skin at right angles. The force of application increases as the researcher advances the probe until the fiber bends. In this study, the participants were instructed to sit still with their eyes closed during the procedure and focus on the tactile sensation. The procedure was repeated using various weights of fibers, forming an ascending and descending staircase. At each level of the staircase, 10 actual stimulations and 5 catch trials (a total of 15 stimulations) were presented. In each trial, the experimenter asked the participants whether they felt the stimulus, to which they had to respond verbally. The threshold was established at the level when the subjects reported 6 of 10 stimuli correctly.
Two-Point discrimination test. Stimuli were delivered manually to the dominant forearm.
Participants were instructed to sit still with their eyes closed during the procedure discriminate between single and double taps, responding verbally. In this procedure, double or single taps were administered randomly. Only double taps were used to calculate the threshold. The separation between the 2 starting points was 1 and 5 cm in the ascending and descending modes, respectively.
The separation was then decreased by 0.5 cm after each correct response. When an error was made, the separation rose by 0.5 cm. The participants' threshold was derived from the minimum distance that was perceived between the 2 points 5 times consecutively.
Thermal sensitivity. A warming cylinder with 1,5 cm of diameter was placed on the dorsal side of the right forearm and participants were instructed to indicate verbally as soon as the heat became intolerable. To prevent tissue damage, maximum duration of the heat exposure was set at 40sec. The assessment was administered five times and the average of the measurements was used in the analysis.

Image Acquisition
A Philips Achieva scanner operating at 3T and equipped for echo-planar imaging was used to acquire functional magnetic resonance images using 32-channels SENSE head coil. Head movements were minimized with mild restraint and cushioning. Functional MRI images were acquired for the entire cortex using blood-oxygen-level-dependent (BOLD) contrast imaging (38 slices, in-plane resolution = 2.5 x 2.5 mm, slice thickness = 4 mm, repetition time (TR) = 2 s, echo time (TE) = 30 ms, flip angle = 77 deg). For each scan 122 fMR volumes were acquired. We also acquired a three-dimensional high-resolution T1-weighted structural image for each subject (parameters: 342 slices, in-plane resolution = 0.5 x 0.5 mm, slice thickness = 0.5 mm, TR = 2 s, TE = 5.75 ms, flip angle = 8 deg).

Image analysis
The first four volumes of each run were discarded to allow for T1 equilibration. All images were corrected for head movements (realignment) using the first volume as reference. The images of each participant were then coregistered onto their T1 image. Coregistered images were then normalized to the standard MNI-152 EPI template using the mean realigned image as a source.
Images were then spatially smoothed using a 6-mm full-width half-maximum isotropic Gaussian kernel. Functional images were analyzed for each subject separately on a voxel-by-voxel basis according to the general linear model (GLM). Neural activation during the blocks was modeled as a boxcar function spanning the whole duration of the blocks and convolved with a canonical hemodynamic response function, chosen to represent the relationship between neuronal activation and blood oxygenation [12]. Separate regressors were included for Affective vs. Neutral. Inter-block intervals were also modeled in relation to the nature of the previous block (Affective-rest vs.
Neutral-rest). Group analysis was performed on estimated images that resulted from the individual models of each condition (Affective vs. Neutral) compared with its baseline (Affective-rest vs. Neutral-rest), treating subject as a random factor. Figure S1: Experimental setup. Tactile stimulation of the right dominant dorsal forearm was delivered manually with a soft goat's hair brush (2,5 cm wide, 3 cm long). In order to guarantee the highest control of the stimulation, the experimenter wore earphones and was skilled to use acoustic signals to stimulate at the precise velocity and in the correct temporal sequence. Earphones were triggered by a remote computerized metronome, previously programmed to provide the exact velocities. To guide the experimenters during the stimulation, a grid was drawn on the hairy skin of the long axis of the participants' dominant forearm. To minimize CT habituation, four different areas of the forearm delimitated by the grid were stroke (two laterals and two medials; stimulation direction: from proximal to distal).