Using, knowing, owning artifacts: What hoarding behavior and apraxia tell us about human-object relations

Humans have developed exceptional capacities for tool use, such that everyday interactions with the physical world largely involve manufactured objects (i.e., artifacts). Although research on apraxia has elucidated the cognitive mechanisms underlying tool use, human-object relations extend beyond their functional use to include socio-emotional dimensions that remain comparatively understudied. This critical review addresses two syndromes traditionally studied in separate fields that, when considered together, provide insights into the nature of human-object relations. Apraxia is marked by impaired tool use in the absence of hoarding behavior and is associated with lesions to left temporo-parietal regions that disrupt semantic knowledge or technical reasoning. In contrast, hoarding behavior is characterized by difficulties discarding possessions and excessive attachment to objects without tool-use deficits and is linked to neural alterations in a fronto-temporal network centered on the medial prefrontal and cingulate cortex, overlapping with regions implicated in psychological ownership, reward processing, value attribution, and social categorization. Integrating neuropsychological findings with research on psychological ownership, consumer behavior, and social psychology, this review proposes a three-factor neurocognitive model of human-object relations: a "Knowing" component (i.e., semantic tool knowledge), a "Using" component (i.e., technical reasoning), and an original "Owning" component (i.e., psychological ownership and object value). Evidence further suggests a bidirectional relationship between the latter component and action-related domains (e.g., body-object distance, effort justification, perceived control, kinematic parameters, personal object advantage). Reciprocal connections between the three networks may enable the dynamic regulation of context-dependent decisions. This framework opens new avenues for both clinical and fundamental research.