1. Neural activity in the monkey hippocampal formation (HF) was analyzed during a spatial moving task in which the monkey was guided by auditory and visual cues and when stimuli were presented from various directions. The monkey could control a motorized, movable device (cab) and its route to a target location by pressing the proper one of five available bars in an appropriate sequence (spatial moving task). In any of several locations in the field, neural responses were evident in relation to the presentation of various objects or human movement in some relative direction (left, anterior, right) as a directional stimulus test. 2. Of 238 hippocampal neurons analyzed, 172 (72.3%, 23866) responded in either the spatial moving task, or to the direction from which stimulation was presented, or to the location of the monkey in the field, or to some combination of these. 3. The activity of 79 (33.2%) neurons was higher when the monkey was in some specific location in the field during the spatial moving task, regardless of the approach route or other task parameters (place related neurons). 4. Responses to the task cues in the spatial moving task were evident in 110 (46.3%) neurons (task related neurons). Of these, 77 (32.4%) neurons were not place related. The remaining 33 ( 13.9%) neurons were both task related and place related. These neurons responded to task cues in only that part of the field in which place related responses occurred. The neural response to the task cues disappeared when the monkey moved out of the place response region. The place related and task related neural responses disappeared when the room light was switched off. Thus information from the environment outside of the cab contributed to the place related and task related responses. 5. Stimuli presented from certain specific directions induced responses, selectively, in 41 ( 17.2%) of the neurons (direction related neurons). The dependence of the preferred direction was described in one of three ways-egocentric, allocentric, or place-direction specific. Nineteen egocentric neurons responded to a stimulus only when it was presented from a certain direction relative to the orientation of the monkey, regardless of the location of the monkey. Eleven allocentric neurons responded to a stimulus only when it was presented at a particular position in the room, regardless of the location or orientation of the monkey. . 6. There were 11 place-direction specific type neurons, each of which responded to a stimulus from a specific direction when the monkey was in a specific location in the field and in a specific orientation. All place-direction specific type neurons also had place related responses. The sensitivity to a directional stimulus was restricted to a location in which there was a place related response. The direction selective responses also disappeared when the monkey was rotated to any other than one specific orientation in its region of sensitivity or was moved to some other location even in the same orientation. This observation suggests that environmental space cue perception in both egocentric and allocentric coordinates can combine synergistically to induce a place related response in the primate HF. 7. Hippocampal neurons responded to the occurrence of significant events (or episodes) in the place field. This indicates that hippocampal gating of incoming information may depend on where the monkey is located. These responses suggest representation related to episodic memory and linkage between spatial and non-spatial functions in the HF.
