Abstract Functional Magnetic Resonance Imaging (fMRI) was used to identify a small area in the human posterior fusiform gyrus that responds selectively to faces (PF). In the same subjects, phase-encoded rotating and expanding checkerboards were used with fMRI to identify the retinotopic visual areas V1, V2, V3, V3A, VP and V4v. PF was found to lie anterior to area V4v, with a small gap present between them. Further recordings in some of the same subjects used moving low-contrast rings to identify the visual motion area MT. PF was found to lie ventral to MT. In addition, preliminary evidence was found using fMRI for a small area that responded to inanimate objects but not to faces in the collateral sulcus medial to PF. The retinotopic visual areas and MT responded equally to faces, control randomized stimuli, and objects. Weakly face-selective responses were also found in ventrolateral occipitotemporal cortex anterior to V4v, as well as in the middle temporal gyrus anterior to MT. We conclude that the fusiform face area in humans lies in non-retinotopic visual association cortex of the ventral form-processing stream, in an area that may be roughly homologous in location to area TF or CITv in monkeys. Hum. Brain Mapping 7:29–37
Paper identifies three face responsive area and homologous area in monkey
- The posterior fusiform g. (PF)
- most responsive and selective face area, homologous to lateral TF (considered as a gateway for high level visual information based object processing to each emotional area)
- Medial to PF in the posterior parahippocampal gyrus is an area that selectively responds to non-face objects, and may be homologous to medial TF in monkey.
- Second face-selective area is in the middle temporal gyrus
- correspond to the face-responsiveness
- homologous to superior temporal sulcus in macaque, which implicated in attention
- response was noted superior and anterior to the visual motion area MT, in the middle temporal gyrus
- Third face-selective area (LO) (lies in the cortex that projects to PF), centered anterior to the more foveal part of V4v
- area is selective for objects and animals as well as faces.
- area can be distinguished from PF through its weaker and less face-specific response, in comparison to objects and cars
- in some subject extended into foveal VP and V3A
Significance of results -
- construction of a neural model of face processing, requires that PF be located relative to other areas in the visual processing stream.
- fusiform face area is in a non-retinotopic region of the ventral visual processing stream.
- Suggests human brain face perception capability is evolved from our common ancestor with the old world monkeys, the high order visual processing areas have shifted postero-ventrally and differentiated, while maintaining their topographical relations and general functional specializations.
Homologous analysis of human face perception area with monkey
- In macaques, the highest concentrations of face selective neurons have so far been found in the anterior superior temporal polysensory (STPa) and dorsal anterior infero-temporal (AITd) areas.
- Anatomically, macaque STPa and AITd lie in the anterior part of the superior temporal sulcus (STS), dorsal and anterior in the temporal lobe, adjacent to auditory association cortex.
- In contrast, human PF lies ventral and posterior in the temporal lobe, adjacent to limbic cortex of the parahippocampal gyrus.
- if the homologies between the visual cortices of humans and macaques are only approximate, the general location of PF relative to retinotopic areas, and relative to the dorsal vs. ventral streams, would still have important implications. Specifically, if the human PF is homologous to the macaque STS, then it should lie in a nonretinotopic area more associated with the dorsal stream. Conversely, if PF is homologous to the macaque V4v, then it should lie in retinotopic cortex of the ventral stream.
Location of PF in human and significance
- PF in a retinotopic area (e.g., human V4v) - imply that the calculations that it performs to detect faces are relatively low-level.
- PF in non-retinotopic regions - ( i.e. farther in the ventral stream) would imply the input would include color and form information, and it would project to anteromedial temporal areas where memories and emotions associated with the face may be elaborated.
- PF is in the dorsal stream - imply less sensitivity to the fine structure of the face and more to its location and movement, or the location and movement of its parts.
Retinotopic visual areas were mapped in the same subjects using fMRI to measure the polar angle and eccentricity of each location in the visually responsive areas. Polar angle was measured using a rotating wedge of flickering black-and-white checks; eccentricity was measured using an expanding ring of flickering checks.
bilateral sequence of activation in PF 13 out of 14 hemispheres.
all subjects, the highest level of face-selective activation was in the base of the posterior fusiform gyrus.
Identification of PF : Talairach coordinates are similar to those that have been reported for face-selective responses in PF by other studies using PET [Sergent, 1993; Haxby et al., 1994], fMRI [Puce et al., 1995; Clark et al., 1996; Kanwisher et al., 1996],MEG[Halgren et al., submitted], and intracranial EEG [Halgren et al., 1994].
phase encoding in the same normal subjects was used to identify the retinotopic visual areas areas V1, V2, V3, V3A, VP, and V4v. In all 13 hemispheres, PF was located anterior to the ventral part of visual area V4v. data clearly indicate that PF is not in retinotopic cortex, as typically defined.
Moving low-contrast concentric rings were used in the same subjects to activate the visual motion area MT and the adjacent area MSTd. PF was found to lie substantially more ventral than these areas. Since MT1 is the most ventral outpost in the dorsal stream, this supports the idea that PF is in the ventral visual stream.
Weak retinotopy between V4v and PF.suggested the presence of interposed visual area with weaker retinotopic color-sensitive area in the same general region. Previous fMRI and Pet study locates the color area posterior to the face area.
These attribute make it V4v homologous to PITv. PITv lies just anterior to V4v in macaques, if true then PF would be homologous to the area just anterior to PITv.
- results in two candidate
- CITv ventrolaterally and TF ventromedially.
- in macaques, TF lies substantially ventral to MT, as does PF in humans according to our data.
- TF and PF , have similar gross anatomical location and cytoarchitectonics
- The fusiform g. in humans and area TF in macaques both lie immediately lateral to the collateral sulcus, and the face-selective part of the fusiform g. in humans and area TF in macaques both lie at about the level of the posterior limit of the corpus callosum.
- the cellular architecture of the fusiform gyrus at this level in humans is distinctive, and is similar to that of TF in macaques.
- results in two candidate
The fMRI response to grayscale face photographs was also compared in four subjects to that evoked by grayscale images of objects and of cars, and black-onwhite sketches of faces
- All of the retinotopic visual areas were strongly activated by all four stimulus categories.
- no difference was found in the response of V4v to the faces as compared to objects, providing further evidence that the face-selective area does not correspond to V4v.
- MT appeared to respond weakly to the stimuli, again with no differentiation between the stimulus categories.
- the fMRI response in PF, was much greater to faces as compared to objects or cars.
The selectivity of PF for faces in this task is striking given that the sensory characteristics of the face photographs are clearly more similar to those of the car photographs than to those of the face sketches, whereas the face-selective responses are to faces regardless of whether they are photographs or sketches.
PC (posterior collateral): An area similar in shape and size to PF but more responsive to nonface objects and cars was identified medial to PF,
- imply that PF and PC are parts of the same cortical area, involved in the categorical encoding of complex visual stimuli.
- like medial TF in monkey
- PC lies just anterior to the part of V4v that maps the most dorsal part of the visual field.
- PC is just lateral to the subicular complex in the posterior parahippocampal gyrus, a limbic area with very distinctive cellular architecture in the medial part of the parahippocampal g.
- TH in monkey does not receive visual input but input from auditory association cortex. so TH cannot be compared to PC.
Note: Fig is directly referred from the paper , is used for better understand of the paper.
 Halgren, E., Dale, A. M., Sereno, M. I., Tootell, R. B., Marinkovic, K., & Rosen, B. R. (1999). Location of human face-selective cortex with respect to retinotopic areas. Human brain mapping, 7(1), 29-37.