Neural correlates of social and non-social personal space intrusions: Role of defensive and peripersonal space systems in interpersonal distance regulation

Figures & data

Figure 1. On the left panel, stimuli used in the experimental tasks. All stimuli were flipped horizontally, resulting in 24 unique images (12 non-social and 12 social, 12 high threats and 12 low threats). On the right panel, ratings of Arousal, Dangerousness, and Unpleasantness provided by an independent sample (N = 24). Error bars represent the standard deviation from the mean. *** p < .001.

Figure 2. (a). Schematic representation of the fMRI task, wherein participants passively viewed non-social and social stimuli of different threat levels move towards (Approach) or away (Withdrawal) from them, and rated their discomfort level. Non-social condition is displayed. (b). Schematic representation of the computerized distance task, wherein participants manipulated the distance from social and non-social stimuli by adjusting their size on the screen. Non-social condition is displayed. (c). Behavioral responses in the computerized distance task showed greater distances for high relative to low threat stimuli, and for non-social relative to social stimuli. *** p< .001.

Table 1. Descriptive statistics (mean and standard deviation in brackets) for discomfort ratings during the fMRI task, distance in the computerized task, and preferred distance (m) in the “Stop-distance” task. Discomfort ratings were provided in a 1–5 scale; distance in the computerized task was operationalized as the inverse of the percentage of maximum image size (such that values vary from 0 to 100 and greater values represent greater distance); distance in the “stop-distance” task is provided in meters.

		Discomfort
	Preferred Distance	Approach	Withdrawal
fMRI task
Non-social low threat		2.50 (0.97)	1.87 (0.72)
Non-social high threat		3.55 (1.11)	2.76 (1.04)
Social low threat		2.04 (0.87)	1.47 (0.44)
Social high threat		2.67 (1.01)	1.99 (0.59)
Computerized distance task
Non-social low threat	80.71 (20.03)
Non-social high threat	84.48 (17.59)
Social low threat	64.81 (13.51)
Social high threat	71.35 (13.48)
“Stop-distance” task
Experimenter	0.83 (0.23)
Tarantula	1.47 (0.85)

Table 2. Brain regions displaying greater activation for moving (A) and static (B) social relative to non-social stimuli, and non-social relative to social stimuli, controlling for level of discomfort. (FDR p < .05; MNI coordinates of the peak voxel are reported).

	R/L	k	x	y	z	T	BA
Moving (Approach/Withdrawal)
Social > Non-social
Cuneus, lingual gyrus	R	3147	8	−92	16	6.00	18
Fusiform face area	R	795	40	−84	−12	8.67	37
Temporo-parietal junction	L	217	−44	−72	20	4.36	39
Calcarine sulcus	L	185	−16	−72	16	3.77	18
Fusiform face area	L	317	−42	−56	−22	5.37	37
Temporo-parietal junction	R	601	50	−52	4	5.65	39
Superior temporal gyrus	L	274	−52	−52	8	4.40	22
Medial prefrontal cortex	L	106	−18	62	10	4.03	10
Non-social > Social
Middle occipital gyrus	L	1436	−32	−94	−4	6.73	18
Middle occipital gyrus	R	1058	38	−86	8	5.57	19
Fusiform gyrus	R	272	26	−62	14	4.44	19
Fusiform gyrus	L	132	−30	−58	−12	4.56	19
Static (Near/Far)
Social > Non-social
Calcarine sulcus	L	4487	0	−94	10	7.03	18, 19, 31, 30, 17, 23
Fusiform face area	R	728	40	−84	−12	9.24	37, 19, 18
Fusiform gyrus	L	249	−36	−82	−18	5.57	19
Fusiform face area	L	144	−42	−56	−22	6.34	37
Temporo-parietal junction	R	385	50	−54	8	4.51	39, 22
Ventromedial prefrontal cortex	R	294	6	48	−16	4.93	11, 10
Non-social > Social
Middle occipital gyrus	R	622	52	−76	2	5.07	19
Middle occipital gyrus	L	950	−54	−72	0	5.81	37
Middle occipital gyrus	L	108	−26	−62	32	3.83	39
Fusiform gyrus	R	168	32	−50	−12	4.38	19
Fusiform gyrus	L	203	−26	−48	−16	5.12	19

Table 3. Brain regions displaying greater activation for Approach > Withdrawal, and Withdrawal > Approach (A), and results of the conjunction analyses (B) (FDR p < .05; MNI coordinates of the peak voxel are reported).

	R/L	k	x	y	z	T	BA
Contrast
Approach > Withdrawal
Middle occipital gyrus extending to superior parietal lobule	L/R	138,970	−22	−82	−10	15.20	7, 17, 18, 19, 20, 37, 39
Thalamus	L	411	−20	−30	−2	7.79
Midbrain	R	155	6	−30	−4	7.08
Precentral gyrus	L	154	−30	−8	46	4.37	6
Premotor extending to dorsolateral prefrontal cortex	R	1168	42	12	28	7.25	6, 9, 46
Insula	R	74	30	24	2	4.04	13
Withdrawal > Approach
Cerebellum (Crus 1)	R	444	18	−94	−24	4.67
Middle occipital gyrus, extending to parietal and temporal	R	9985	30	−68	4	9.95	19
Angular gyrus	R	1849	42	−60	40	5.45	39, 40
Superior temporal gyrus	R	1616	66	−30	4	5.18	22
Brainstem	L	485	−8	−30	−50	4.63
Postcentral gyrus	R	333	20	−30	62	4.27	2
Middle frontal gyrus	R	362	30	12	52	4.25	6
Middle frontal gyrus	L	375	−40	18	46	4.13	8
Conjunction
(Non-social High threat Approach > Withdrawal) ˄ (Social High threat Approach > Withdrawal)
Middle occipital gyrus	L	6876	−22	−82	−12	9.64	17, 18, 19, 20, 37, 39
Superior parietal lobule	L	74	−22	−60	54	4.24	7
Superior parietal lobule	R	159	26	−60	56	4.23	7
Midbrain	L	67	−2	−32	−4	4.77
Premotor extending to dorsolateral prefrontal cortex	R	235	44	12	28	4.86	6, 9, 46
(Non-social High threat Withdrawal > Approach) ˄ (Social High threat Withdrawal > Approach)
Cuneus, precuneus, posterior cingulate	L/R	1083	0	−86	34	6.17	7, 18, 19
Middle occipital gyrus	L	177	−28	−68	2	4.39	7, 18, 19
Angular gyrus	L	117	−48	−60	26	4.11	22, 40
Angular gyrus	R	446	48	−60	46	4.04	40
Superior temporal gyrus	R	150	66	−28	4	4.20	22

Figure 3. (a). Brain regions showing increased activation for social relative to non-social stimuli (left), and for non-social relative to social stimuli (right), irrespective of threat level and direction of movement. (b). Brain regions showing increased activation for social relative to non-social stimuli (left), and to non-social relative to social stimuli (right), irrespective of threat level and distance. TPJ = temporoparietal junction; FFA = face fusiform area; MPFC = medial prefrontal cortex. Activation threshold set at cluster-forming p< .001 uncorrected, and FDR-corrected p< .05 at the cluster level. Results in the figure are displayed at p< .005 uncorrected for visualization purposes, but only clusters surviving at the predefined threshold are highlighted.

Figure 4. (a). Brain regions showing increased activation for approaching relative to withdrawing stimuli (left), and for withdrawing relative to approaching stimuli (right), irrespective of stimulus category and threat level. (b). Left: Results of the conjunction analysis showing the overlap on the midbrain between (non-social threats approach > withdrawal) and (social threats approach > withdrawal). Right: Results of the conjunction analysis showing the overlap on the vlPFC between (non-social threats withdrawal > approach) and (social threats withdrawal > approach). PMv = ventral premotor cortex; SPL = superior parietal lobule; vlPFC = ventrolateral prefrontal cortex (*significant at p< .005 uncorrected, FDR-corrected p< .05); PCC = posterior cingulate Activation threshold set at cluster-forming p< .001 uncorrected, and FDR-corrected p< .05 at the cluster level. Results in the figure are displayed at p< .005 uncorrected for visualization purposes, but only clusters surviving at the predefined threshold are highlighted.

Table 4. Brain regions displaying greater activation for Near > Far, and Far > Near (FDR p < .05; MNI coordinates of the peak voxel are reported).

	R/L	k	x	y	z	T	BA
Near > Far
Middle Occipital gyrus	L	23,338	−10	−100	10	17.56	7, 17, 18, 19, 20, 30, 31, 37
Superior parietal lobule	L	421	−30	−60	58	5.07	7
Thalamus	R	133	20	−28	−4	6.70
Thalamus	L	153	−20	−28	−4	5.15
Precentral gyrus	R	92	32	−2	52	4.20	6
Dorsolateral prefrontal cortex	R	604	46	10	30	4.69	9, 46
Inferior frontal gyrus/Insula	L	119	−42	20	−8	3.86	47
Inferior frontal gyrus/Frontal pole	L	225	−46	50	−6	4.08	10
Far > Near
Middle occipital gyrus	L	178	−28	−100	−4	7.37	18

Figure 5. (a). Brain regions showing increased activation for near relative to far stimuli (left), and for far relative to near stimuli, irrespective of stimulus category and threat level. (b). Left: Results of the conjunction analysis showing the overlap on the midbrain between (non-social threats near > far) and (social threats near > far). Activation threshold set at cluster-forming p< .001 uncorrected, and FDR-corrected p< .05 at the cluster level. Results in the figure are displayed at p< .005 uncorrected for visualization purposes, but only clusters surviving at the predefined threshold are highlighted.

Table 5. Results of the PPI analysis, showing brain regions with increased functional connectivity with the midbrain PAG in response to approaching social versus non-social stimuli (FDR p < .05; MNI coordinates are reported).

	R/L	k	x	y	z	T	BA
Social > Non-social
Dorsolateral prefrontal cortex	R	191	42	32	28	4.47	9
Superior frontal gyrus (premotor cortex)	R	174	24	24	56	5.98	6, 8
Superior frontal gyrus (premotor cortex)	L	107	−12	32	60	5.73	6, 8

Figure 6. (a). Brain regions showing increased functional connectivity with the midbrain for approaching social relative to non-social stimuli. (b). Scatter plot depicting the correlation between preferred distance to social stimuli in the computerized task, and connectivity strength between the midbrain and the left PMd. Activation threshold set at cluster-forming p< .001 uncorrected, and FDR-corrected p< .05 at the cluster level. Results in the figure are displayed at p< .005 uncorrected for visualization purposes, but only clusters surviving at the predefined threshold are highlighted.