Courses:

M1 (F1) – Area 5 (PE) Circuit

• skeletomotor circuit
• segmenting actions planned by other motor areas into elementary movements
• unique in controlling independent finger movements

F4 (PMC) (behind arcuate) – VIP Circuit

• arm, neck, face, mouth not distal extremities
• tactile RFs or tactile and visual
• this is Graziano-Gross: visual fields anchored to the body part
• transforming peri-personal space coordinates so can move toward objects

PMv (F5ab) – AIP Circuit

• “grasp” neurons – fire in relation to movements of hand prehension necessary to grasp object
• transforms the intrinsic properties of the objects into the appropriate hand movements – tool use
• inactivation prevents/disrupts preshaping of the hand during grasping

PMv (F5c) – PF Circuit

• F5c neurons: mirror neurons
• discharge when the monkey observes another individual performing an action similar to that encoded by the neuron (Rizzolatti)
• grasping, placing or manipulating object
• suggest cognitive representation of the grasp, placing
• action imitation and action recognition
• has → for speech...

PMd (F2) – Parietal Circuit

• PMd set-related (anticipatory) activity
• connections with medial IP sulcus where Iriki (196) recorded “croupier neurons”
• RFs expand when monkey used rake to pull in object/food
• plasticity of RF properties

PMd (F2/F7) – Parietal Circuit

• rapidly learn arbitrary stimulus-response associations
• Passingham group showed lesions in PMd prevent arm movements made accessible to different colored stimuli
• many subsequent studies
• role in conditional movement selection

SMA (F3) – PEci Circuit

• some still say related to postural adjustments
• Tanji group shows many SMA neurons fire in relation to particular sequences of movements

Pre-SMA (F6)

• inputs are from rCing and PFC
• Tanji – learning new sequences
• Hikosaka – learning new sequences
• motivation?

Rostral Cingulate Motor Area

• Tanji shows related to action selections based on reward

The Neural Control of Visually Guided Eye Movements

I. The Classification of Eye Movements

The retina is specialized in having only a small region of tightly packed photoreceptors called the fovea. This region affords high-acuity vision. To be able to see fine detail in the visual scene, we therefore have to repeatedly shift the direction of our gaze.

Two general classes of eye movements have been distinguished: Conjugate eye movements and vergence eye movements. Conjugate eye movements are of two types: saccadic and smooth pursuit.

• The function of saccadic eye movements is to rapidly acquire objects in the visual scene for central viewing so that they may be analyzed in detail.
• The function of the smooth pursuit system is to maintain a moving object in central view as in the case of tracking a bird in flight.

For the most part different neural mechanisms control saccadic and smooth pursuit eye movements. Research in the Schiller Lab is concerned predominantly with the neural control of visually guided saccadic eye movements.

II. Subcortical Mechanisms of Visually Guided Saccadic Eye Movements

Temporal trace of vertical eye movements and the discharge of a neuron in the monkey oculomotor nucleus that innervates the inferior rectus. The maintained activity of the neuron during fixations is proportional to the angular deviation of the eye in orbit. Brief, high frequency bursts result in downward saccadic eye movements; the longer the burst, the larger the saccade. We refer to the coding operation here as a rate code.

The central subcortical structure involved in the generation of visually guided saccadic eye movements is the superior colliculus. It resides on the roof of the midbrain and is about the size of a pea. As in most visual structures, the contralateral visual hemifield is laid out in an orderly fashion in the structure.

Neurons in the upper layers of the superior colliculus have well-defined receptive fields. Neurons in the deeper layers discharge prior to and during eye movements; some of these cells also have visual receptive fields. Electrical stimulation here elicits saccades at low currents.

III. Cortical Mechanisms of Visually Guided Saccadic Eye Movements

Numerous cortical areas are involved in the generation of saccadic eye movements. The monkey brain and the major regions from which electrical stimulation elicits saccadic eye movements. The insets show the saccades elicited with the dots representing the direction of the gaze prior to stimulation. At most sites the saccades produced have a fixed vector. What that vector is depends on where one stimulates within the structure just as in the superior colliculus. The visual field representation and the saccadic vectors produced are laid out in a neat topographic order within each structure. Exceptions to vector representation are seen in a frontal region called the medial eye fields (MEF) and in parts of parietal cortex. In these areas the final positions of the eye in orbit is coded, hence called a place code. There is an orderly representation of these positions within these structures.

How do the signals from the various cortical areas reach the brainstem oculomotor centers?

In summary, electrical stimulation in the lower layers of V1 and V2 produces facilitation, whereas in the upper layers it produces interference. In LIP both of these effects can be obtained in different subregions. In addition, at those sites where cells discharge with fixation, stimulation prolongs fixation time. In the medial and frontal eye fields only facilitatory effects were found. Lastly, in V4 electrical stimulation was ineffective.

The next step in learning more about target selection with eye movements entailed examination of the consequences of local injection of pharmacological agents into various brain areas. To accomplish this, electrodes were devised that enabled us to first record or stimulate and to then inject selected agents. After establishing the location of the visual or motor field of the neurons two targets were presented with one centered in the field. Data were then collected before, during and after injecting pharmacological agents in minute quantities.

Symposium: New Approaches in Neuroscience

Sponsored by the McGovern Institute for Brain Research at MIT, May 2002

Novel Avenues for Electrophysiology (Chair: Emilio Bizzi)

Speakers:

Marcus Meister (Harvard University): "The Neural Code of the Retina"

Miguel Nicolelis (Duke University): "Action from Thoughts: Building Brain-Machine Interfaces to Restore Neurological Function"

Richard Andersen (Caltech): "A Neural Correlate of Intention and its Potential for Controlling Prosthetics Systems"

Mahlon R. DeLong (Emory University): "Deep Brain Stimulation for Movement Disorders"

Genes in Neuroscience (Chair: H. Robert Horvitz)

Speakers:

Lawrence Salkoff (Washington University): "The Conserved Family of Voltage-Gated Ion Channels in C. elegans"

Joseph Takahashi (Northwestern University): "Molecular Genetics of Circadian Clocks in Mammals"

Catherine Dulac (Harvard University): "Molecular Biology of Pheromone Detection: from genes to behavior"

Connie Cepko (Harvard Medical School): "Genomic Approaches to Photoreceptor Development and Disease"