Neuroscience Exploring the Brain 3 e Chapter 10

Introduction • Neurons in the visual system – Neural processing results in perception • Parallel pathway serving conscious visual perception originate in the retina – Progress to lateral geniculate nucleus, primary visual cortex & higher order visual areas in temporal and parietal lobes • Overlapping neuronal receptive fields – Sensitive to different facets of the visual input Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Retinofugal Projection • The Optic Nerve, Optic Chiasm, and Optic Tract Copyright ©

The Retinofugal Projection • Right and Left Visual Hemifields – Left hemifield projects to right side of brain – Ganglion cell axons from nasal retina cross, temporal retinal axons stay ipsilateral Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Retinofugal Projection • Visual deficits from lesions in the retinofugal projection Copyright ©

The Retinofugal Projection • Nonthalamic Targets of the Optic Tract: – Hypothalamus: Biological rhythms, including sleep and wakefulness – Pretectum: Size of the pupil; certain types of eye movement – Superior colliculus: Orients the eyes in response to new stimuli Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Lateral Geniculate Nucleus (LGN) Copyright © 2007 Wolters Kluwer Health | Lippincott Williams

The Lateral Geniculate Nucleus (LGN) • Inputs Segregated by Eye and Ganglion Cell Type

The Lateral Geniculate Nucleus (LGN) • Receptive Fields – Receptive fields of LGN neurons: Identical to the ganglion cells that feed them – Magnocellular LGN neurons: Large, monocular receptive fields with transient response – Parvocellular LGN cells: Small, monocular receptive fields with sustained response Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Lateral Geniculate Nucleus (LGN) • Nonretinal Inputs to the LGN – Primary visual cortex provides 80% of the synaptic input to the LGN – Brain stem neurons provide modulatory influence on neuronal activity Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex Copyright © 2007 Wolters Kluwer Health | Lippincott Williams

Anatomy of the Striate Cortex • Retinotopy – Map of the visual field onto a target structure (retina, LGN, superior colliculus, striate cortex) – Central visual field overrepresented – Discrete point of light: Activates many cells in the target structure due to overlapping receptive fields – Perception: Based on the brain’s interpretation of distributed patterns of activity Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Retinotopy Copyright © 2007 Wolters Kluwer Health |

Anatomy of the Striate Cortex • Lamination of the Striate Cortex – Layers I - VI – Spiny stellate cells: Spinecovered dendrites; layer IVC – Pyramidal cells: Spines; thick apical dendrite; layers III, IV , V, VI – Inhibitory neurons: Lack spines; All cortical layers; Form local connections Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Inputs to the Striate Cortex – Magnocellular LGN neurons: Project to layer IVC – Parvocellular LGN neurons: Project to layer IVC – Koniocellular LGN axons: Bypasses layer IV to make synapses in layers II and III Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Ocular Dominance Columns – Studied with transneuronal autoradiography from retina, to LGN, to striate cortex. Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Ocular Dominance Columns – Present in layer IV of macaque monkeys - alternating inputs from two eyes Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Inputs to the Striate Cortex – First binocular neurons found in striate cortex - most layer III neurons are binocular (but not layer IV) Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Outputs of the Striate Cortex: – Layers II, III, and IVB: Projects to other cortical areas – Layer V: Projects to the superior colliculus and pons – Layer VI: Projects back to the LGN Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Monocular Receptive Fields – Layer IVC: Similar to LGN cells – Layer IVC : Insensitive to the wavelength – Layer IVC : Center-surround color opponency • Binocular Receptive Fields – Layers superficial to IVC: First binocular receptive fields in the visual pathway – Two receptive fields - one for each eye Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Cortical Receptive Fields – Orientation Selectivity Copyright ©

Physiology of the Striate Cortex • Cortical Receptive Fields – Direction Selectivity • Neuron fires action potentials in response to moving bar of light Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Cortical Receptive Fields – Simple cells: Binocular; Orientation-selective; Elongated on-off region with antagonistic flanks responds to optimally oriented bar of light – Possibly composed of three LGN cell axons with center-surround receptive fields Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Cortical Receptive Fields – Complex cells: Binocular; Orientation-selective; ON and OFF responses to the bar of light but unlike simple cells, no distinct on-off regions Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Cortical Receptive Fields – Blob Receptive Fields: • Circular • Monocular • No orientation or direction selectivity • Majority of color-sensitive neurons outside layer IVC • Specialized for analysis of object color Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Physiology of the Striate Cortex • Parallel Pathways: Magnocellular; Koniocellular; Parvocellular Copyright © 2007

Physiology of the Striate Cortex • Cortical Module – Each module capable of analyzing every aspect of a portion of the visual field Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Beyond Striate Cortex • Dorsal stream – Analysis of visual motion and the visual control of action • Ventral stream – Perception of the visual world and the recognition of objects Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Beyond Striate Cortex • The Dorsal Stream (V 1, V 2, V 3, MT, MST, Other dorsal areas) – Area MT (temporal lobe) • Most cells: Direction-selective; Respond more to the motion of objects than their shape – Beyond area MT - Three roles of cells in area MST (parietal lobe) • Navigation • Directing eye movements • Motion perception Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Beyond Striate Cortex • The Ventral Stream (V 1, V 2, V 3, V 4, IT, Other ventral areas) – Area V 4 • Achromatopsia: Clinical syndrome in humanscaused by damage to area V 4; Partial or complete loss of color vision – Area IT • Major output of V 4 • Receptive fields respond to a wide variety of colors and abstract shapes Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

From Single Neurons to Perception • Visual perception – Identifying & assigning meaning to objects • Hierarchy of complex receptive fields – Retinal ganglion cells: Center-surround structure, Sensitive to contrast, and wavelength of light – Striate cortex: Orientation selectivity, direction selectivity, and binocularity – Extrastriate cortical areas: Selective responsive to complex shapes; e. g. , Faces Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

From Single Neurons to Perception • From Photoreceptors to Grandmother Cells – Grandmother cells: Face-selective neurons in area IT? – Probably not: Perception is not based on the activity of individual, higher order cells • Parallel Processing and Perception – Groups of cortical areas contribute to the perception of color, motion, and identifying object meaning Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Concluding Remarks • Vision – Perception combines individually identified properties of visual objects – Achieved by simultaneous, parallel processing of several visual pathways • Parallel processing – Like the sound produced by an orchestra of visual areas rather than the end product of an assembly line Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

End of Presentation Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Anatomy of the Striate Cortex • Cytochrome Oxidase Blobs – Cytochrome oxidase: mitochondrial enzyme used for cell metabolism – Blobs: Cytochrome oxidase staining in striate cortex – Each blob centered on an ocular dominance column in layer IV – Receive koniocellular inputs from LGN Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins