The pupil light reflex (PLR) is the first and most fundamental mechanism for light adaptation. Here, we address this question by investigating whether microstimulation of the primate PFC is capable of modulating the action of a basic brainstem reflex. However, the extent to which the PFC regulates the action of identified stimulus–response circuits remains unknown. For example, the same region in PFC both transmits motor commands to the brainstem ( Schlag-Rey et al., 1992) and modulates visual activity in posterior visual cortex ( Moore and Armstrong, 2003 Armstrong et al., 2006 Ekstrom et al., 2008). At the highest level of the CNS, the prefrontal cortex (PFC) is thought add flexibility to stimulus–response mappings ( Miller and Cohen, 2001). However, it is unclear whether these motifs are also present within the CNS. Subsumption architectures are ubiquitous in modern robotics and circuit motifs that resemble subsumption architectures are common in interactions between the CNS and peripheral reflexes ( Krasne and Wine, 1975 Vu et al., 1993 Büschges and Manira, 1998 Delcomyn, 1999 Kimura et al., 2006). This precise mechanism-when a higher-order structure without the capacity to produce an action directly modulates information processing in a more basic circuit-has been referred to as a “subsumption architecture” ( Brooks, 1986). One circuit motif that can address this challenge is the development of flexible control systems that regulate existing stimulus–response circuits ( Krasne and Wine, 1975 Brooks, 1986 Prescott et al., 1999). Nervous systems must evolve complex and flexible capacities without sacrificing their basic competencies.
These results suggest that control structures such as the PFC can add complexity and flexibility to even a basic brainstem circuit. Here, we report that microstimulation in the prefrontal cortex (PFC) modulates the gain of the PLR, changing how a simple reflex circuit responds to physically identical stimuli. The neural bases of these modulations are unknown. Although it is often described in textbooks as being an immutable reflex, converging evidence suggests that the magnitude of the PLR is modulated by cognitive factors. SIGNIFICANCE STATEMENT The pupil light reflex (PLR) is our brain's first and most fundamental mechanism for light adaptation. These results provide evidence of the selective regulation of a basic brainstem reflex by the PFC. The spatial specificity of this effect parallels the effect of FEF stimulation on attention and suggests that FEF is capable of modulating visuomotor transformations performed at a lower level than was previously known. FEF microstimulation enhanced the PLR to probes presented within the stimulated visual field, but suppressed the PLR to probes at nonoverlapping locations. We show that microstimulation of the rhesus macaque FEF alters the magnitude of the PLR in a spatially specific manner. Although the neural basis of these modulations remains unknown, one possible source is the PFC, particularly the frontal eye field (FEF), an area of the PFC implicated in the control of attention. However, emerging behavioral evidence suggests that the PLR may be modulated by cognitive processes.
Unlike pupil size, which depends on the interaction of multiple physiological and neuromodulatory influences, the PLR reflects the action of a simple brainstem circuit. One canonical example of a central reflex is the pupil light reflex (PLR): the automatic constriction of the pupil in response to luminance increments. However, the scope of that control remains unknown: it remains unclear whether the PFC can modulate basic reflexes. The prefrontal cortex (PFC) is thought to flexibly regulate sensorimotor responses, perhaps through modulating activity in other circuits.
0 kommentar(er)
