Table 1.
A simplified summary of some of the major sensory receptors and isomorphic pathways leading to sensory mental images.
| Isomorphic templates | |||
|---|---|---|---|
| Sensory domain, receptor type | First order multipolar | Second order | Third order* isomorphism, image type |
| Vision, photoreceptors: rods and cones | Retina = retinal ganglion cells | Thalamus = lateral geniculate, optic tectum* | Primary visual cortex (V1), retinotopic, visual images |
| Somesthetic senses, mechanoreceptors | Dorsal column nuclei (trunk), sensory trigeminal nerve nuclei (face) | Thalamus = VPL and VPM, tectum* | Primary somatosensory cortex (SI), somatotopic, somatosensory images |
| Pain, nociceptors | Dorsal horn lamina I (trunk), sensory trigeminal nuclei (face) | Thalamus = VPL/VPM, VMpo, tectum* | SI and insula-anterior cingulate, somatotopic-homeostatic, pain images |
| Olfaction, chemoreceptors: olfactory sensory neurons | Olfactory bulb = glomeruli: mitral cells | Olfactory cortex | Orbitofrontal cortex, chemotopic, olfactory images. |
| Hippocampus and dentate gyrus, olfactory images | |||
| Gustation, chemoreceptors: taste cells | Gustatory nucleus | Thalamus = VPMpc, tectum* | Anterior insula/frontal operculum, chemotopic, taste images |
| Audition, mechanoreceptors: inner hair cells | Cochlear nuclei | Thalamus = medial geniculate, inferior colliculus, tectum* | Primary auditory, cortex, tonotopic, auditory images |
| Equilibrium, mechanoreceptors: hair cells | Vestibular nuclei | Thalamus = multiple thalamic nuclei, tectum* | Primary vestibular cortex (parieto-insular vestibular cortex: PIVC), images of body position and motion |
Here the third-order telencephalic areas are listed for mammals, but higher levels also exist: Heteromodal association cortices (also designated as high-order association cortex, polymodal cortex, multimodal cortex, polysensory areas, and supramodal cortex) serve as fourth-order integration zones, and in the human brain they include the posterior and anterior parietal cortex, lateral temporal cortex, prefrontal cortex, and portions of the parahippocampal gyrus (Mesulam, 2000). In birds, the third and fourth orders also are in the pallium (Butler et al., 2005, 2011). In fish and amphibians, by contrast, the optic tectum is where the isomorphic visual, somatosensory, auditory, vestibular and nociceptive templates and images are best documented, as are the multimodal images (Echteler, 1985; McHaffie et al., 1989; Stein and Meredith, 1993; Merker, 2005, 2007; Dicke and Roth, 2009; Wullimann and Vernier, 2009a).