Persons with spinal cord injury (SCI), particularly [cervical injuries (tetraplegia]), are unable to effectively regulate core body temperature (Tcore) due to interruption of motor, sensory, and sympathetic pathways. Thus, control of distal extremity vasoconstriction (heat conservation) and shivering thermogenesis (heat production) are impaired, and the ability to maintain a constant Tcore is compromised. Persons with tetraplegia often report “feeling cold,” frequently present with subnormal Tcore (35-36.5°C), and are particularly vulnerable to hypothermia (Tcore<35°C) and associated impairment in cognitive performance, even when exposed to temperatures that are comfortable for able-bodied (AB) individuals. Cool seasonal temperatures have been shown to have a greater adverse effect on personal comfort, activities of daily living (ADLs), and vital daily activities in persons with tetraplegia than that of AB controls. Conversely, a minimal increase in Tcore from subnormal to normothermia, secondary to ambient heat may improve cognitive performance. Interventions addressing the tendency to poikilothermia and enhanced vulnerability to hypothermia in persons with [tetraplegia] are limited. Therefore, exploration of safe and efficacious bioengineering solutions to address the physiological, cognitive, and quality of life (QoL) issues associated with the routine exposure to cool temperatures that persons with [tetraplegia] often encounter is warranted. The goals of this pilot study in persons with [tetraplegia] are: 1) to study the safety and tolerability of a feedback-controlled heated vest and then 2) to study the efficacy of this heated vest to minimize the expected decline in Tcore and associated deterioration of cognitive performance during 2 hours of cool exposure. This single-group (persons with [tetraplegia]), two-condition (heated vest, non-heated vest) prospective study is being proposed to compare the physiological and cognitive responses to controlled cool exposure (18°C) with a prototype heated vest vs. a non-heated vest (control condition). [Eight] subjects with [tetraplegia (C3-T1], AIS A and B) and [eight] AB controls will be recruited for study participation. AB subjects will be observed to ensure the safety of the vest, which will be accomplished by determining the temperatures of the vest and subjective thermal sensation of less than “hot” during a cool condition that will be identical to that to which subjects with SCI will be exposed. Subjects with [tetraplegia] will test the efficacy of the heated vest, i.e. preventing the expected decline in Tcore and cognitive performance and increased thermal comfort. Primary Specific Aim: In a cool thermal chamber (18°C), AB controls will wear the heated vest at maximal setting for 120 minutes in the seated position to determine (1) maximum temperatures of all areas of the interior (user’s side) of the heated vest and (2) subjective comfort of the heated vest (safety testing). Primary Hypothese...